/* ===== B737 Study Guide — Design System ===== */

:root {
    --bg: #0d1117;
    --bg-card: #161b22;
    --bg-card-hover: #1c2129;
    --bg-input: #0d1117;
    --border: #30363d;
    --border-focus: #58a6ff;
    --text: #e6edf3;
    --text-muted: #8b949e;
    --text-dim: #484f58;
    --primary: #58a6ff;
    --primary-hover: #79b8ff;
    --accent: #f0883e;
    --success: #3fb950;
    --success-bg: rgba(63, 185, 80, 0.12);
    --error: #f85149;
    --error-bg: rgba(248, 81, 73, 0.12);
    --radius: 12px;
    --radius-sm: 8px;
    --shadow: 0 4px 24px rgba(0, 0, 0, 0.3);
    --transition: 0.2s ease;
}

*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
}

/* ===== Layout ===== */

.app {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 24px 60px;
}

.header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 24px 0 16px;
    border-bottom: 1px solid var(--border);
    margin-bottom: 28px;
}

.logo {
    font-size: 1.5rem;
    font-weight: 800;
    letter-spacing: -0.03em;
    color: var(--text);
}

.logo span {
    color: var(--primary);
}

.header-right {
    display: flex;
    align-items: center;
    gap: 10px;
}

.aircraft-select {
    padding: 6px 16px 6px 12px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    color: var(--text);
    font-family: inherit;
    font-size: 0.85rem;
    font-weight: 600;
    cursor: pointer;
    text-align: center;
    min-width: 100px;
}

.aircraft-select:focus {
    outline: none;
    border-color: var(--border-focus);
}

/* ===== Streak ===== */

.streak-badge {
    display: flex;
    align-items: center;
    gap: 6px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    padding: 6px 14px;
    font-weight: 600;
    font-size: 0.95rem;
}

.streak-icon {
    font-size: 1.1rem;
}

/* ===== Power Button ===== */

.power-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 50%;
    color: var(--text-muted);
    font-size: 1rem;
    cursor: pointer;
    transition: all var(--transition);
    padding: 0;
    line-height: 1;
}

.power-btn:hover {
    color: var(--error);
    border-color: var(--error);
    background: var(--error-bg);
}

/* ===== Screens ===== */

.screen {
    display: none;
}

.screen.active {
    display: block;
    animation: fadeIn 0.25s ease;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(8px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ===== Menu Screen ===== */

.menu-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 60px 0 40px 0;
    gap: 48px;
}

.menu-title {
    text-align: center;
}

.menu-title h2 {
    font-size: 3rem;
    font-weight: 800;
    letter-spacing: -0.03em;
}

.menu-title p {
    font-size: 1.4rem;
    color: var(--primary);
    font-weight: 600;
    margin-top: 4px;
}

.menu-buttons {
    display: flex;
    flex-direction: column;
    gap: 14px;
    width: 100%;
    max-width: 320px;
}

.menu-btn {
    font-size: 1.05rem;
    padding: 16px 28px;
}

.menu-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
    transform: none;
}

/* Study-set buttons: stacked layout — badge (optional), name, meta row.
   `.btn.set-btn` specificity beats the later `.btn` base rule (which sets
   display:inline-flex + centering and would otherwise override these rules). */
.btn.set-btn {
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    justify-content: center;
    gap: 4px;
    text-align: left;
    padding: 14px 20px;
    position: relative;
}

.set-name {
    font-size: 1rem;
    font-weight: 700;
    line-height: 1.3;
}

/* Row of secondary info: question count · progress */
.set-meta {
    display: flex;
    align-items: center;
    gap: 0;
    font-size: 0.8rem;
    font-weight: 400;
    opacity: 0.72;
    flex-wrap: nowrap;
    width: 100%;
}

.set-count::after {
    content: ' · ';
    white-space: pre;
}

.set-progress {
    /* allow progress text to shrink/truncate gracefully if needed */
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    min-width: 0;
}

/* Line 1: set name + "Last studied" pill on the same row. The pill is
   rendered on every button and toggled with visibility (not display), so all
   buttons keep identical height whether or not it's shown. */
.set-title {
    display: flex;
    align-items: center;
    gap: 8px;
    width: 100%;
}

.set-badge {
    font-size: 0.62rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    padding: 2px 8px;
    border-radius: 999px;
    /* On btn-primary (blue bg): dark text on a semi-transparent tint */
    background: rgba(13, 17, 23, 0.22);
    color: inherit;
    border: 1px solid rgba(13, 17, 23, 0.18);
    line-height: 1.5;
    white-space: nowrap;
    flex-shrink: 0;
}

.set-badge--hidden {
    visibility: hidden;
}

/* Study screen — which aircraft + set is active */
.study-set-title {
    font-size: 1.5rem;
    font-weight: 800;
    letter-spacing: -0.02em;
    margin-bottom: 20px;
}

/* Divider between question sets and flashcard decks */
.set-divider {
    height: 1px;
    background: var(--border);
    margin: 6px 0;
}

/* ===== Back Button ===== */

.screen-topbar {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    align-items: center;
    margin-bottom: 20px;
}

.screen-topbar .back-btn {
    margin-bottom: 0;
}

.study-mastery {
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--primary);
    white-space: nowrap;
}

.back-btn {
    display: inline-flex;
    align-items: center;
    gap: 4px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    color: var(--text-muted);
    font-family: inherit;
    font-size: 0.9rem;
    font-weight: 500;
    cursor: pointer;
    padding: 6px 16px;
    margin-bottom: 20px;
    transition: all var(--transition);
}

.back-btn:hover {
    color: var(--text);
    background: var(--bg-card-hover);
    border-color: var(--text-muted);
}

/* ===== Stats Row ===== */

.stats-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
    margin-bottom: 24px;
}

.stat-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 20px;
    text-align: center;
}

.stat-value {
    font-size: 2rem;
    font-weight: 800;
    color: var(--primary);
}

.stat-label {
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-top: 4px;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* ===== Resume Banner ===== */

.resume-banner {
    background: linear-gradient(135deg, rgba(240, 136, 62, 0.1), rgba(240, 136, 62, 0.05));
    border: 1px solid rgba(240, 136, 62, 0.3);
    border-radius: var(--radius);
    padding: 16px 20px;
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 20px;
}

.resume-banner p {
    flex: 1;
    font-weight: 500;
}

/* ===== Config Card ===== */

.config-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 28px;
    margin-bottom: 28px;
}

.config-card h2 {
    font-size: 1.15rem;
    font-weight: 700;
    margin-bottom: 20px;
}

.field-label {
    display: block;
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: 6px;
    margin-top: 16px;
}

.field-label:first-of-type {
    margin-top: 0;
}

.select,
.input {
    width: 100%;
    padding: 10px 14px;
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    color: var(--text);
    font-family: inherit;
    font-size: 0.95rem;
    transition: border var(--transition);
    appearance: none;
}

.select:focus,
.input:focus {
    outline: none;
    border-color: var(--border-focus);
}

.toggle-row {
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
    margin-top: 20px;
    margin-bottom: 24px;
}

.size-presets {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
    align-items: center;
}

.size-btn {
    padding: 8px 16px;
    border: 1px solid var(--border);
    border-radius: 20px;
    background: transparent;
    color: var(--text-muted);
    font-family: inherit;
    font-size: 0.85rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition);
}

.size-btn:hover {
    border-color: var(--text-muted);
    color: var(--text);
}

.size-btn.active {
    border-color: var(--primary);
    color: var(--primary);
    background: rgba(88, 166, 255, 0.08);
}

.size-input {
    width: 64px;
    padding: 8px 10px;
    text-align: center;
    font-size: 0.85rem;
}

.toggle {
    display: flex;
    align-items: center;
    gap: 8px;
    cursor: pointer;
    font-size: 0.9rem;
}

.toggle input[type="checkbox"] {
    width: 18px;
    height: 18px;
    accent-color: var(--primary);
    cursor: pointer;
}

.toggle-label {
    color: var(--text-muted);
    transition: color var(--transition);
}

.toggle input:checked+.toggle-label {
    color: var(--text);
}

.toggle-group {
    display: inline-flex;
    align-items: center;
    gap: 6px;
}

.help-tip {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 16px;
    height: 16px;
    border-radius: 50%;
    border: 1px solid var(--border);
    font-size: 0.68rem;
    font-weight: 700;
    color: var(--text-dim);
    cursor: help;
    position: relative;
    flex-shrink: 0;
    transition: border-color var(--transition), color var(--transition);
}

.help-tip:hover {
    border-color: var(--primary);
    color: var(--primary);
}

.help-tip-text {
    display: none;
    position: absolute;
    bottom: calc(100% + 10px);
    left: 50%;
    transform: translateX(-50%);
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 10px 14px;
    font-size: 0.82rem;
    font-weight: 400;
    color: var(--text-muted);
    width: 220px;
    line-height: 1.6;
    z-index: 200;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
    pointer-events: none;
    white-space: normal;
}

/* Caret */
.help-tip-text::after {
    content: '';
    position: absolute;
    top: 100%;
    left: 50%;
    transform: translateX(-50%);
    border: 6px solid transparent;
    border-top-color: var(--border);
}

.help-tip:hover .help-tip-text {
    display: block;
}

/* ===== Buttons ===== */

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    border: none;
    border-radius: var(--radius-sm);
    font-family: inherit;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition);
    font-size: 0.9rem;
    padding: 10px 20px;
}

.btn-lg {
    padding: 14px 28px;
    font-size: 1rem;
    width: 100%;
    border-radius: var(--radius);
}

#btn-submit {
    margin-top: 16px;
}

.btn-sm {
    padding: 6px 14px;
    font-size: 0.85rem;
}

.btn-primary {
    background: var(--primary);
    color: #0d1117;
}

.btn-primary:hover {
    background: var(--primary-hover);
    transform: translateY(-1px);
}

.btn-accent {
    background: var(--accent);
    color: #0d1117;
}

.btn-accent:hover {
    opacity: 0.9;
}

.btn-lg:active {
    transform: scale(0.98);
}

.btn:disabled,
.btn.disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.btn-primary:active {
    opacity: 0.9;
}

.btn-ghost {
    background: transparent;
    color: var(--text-muted);
    border: 1px solid var(--border);
}

.btn-ghost:hover {
    color: var(--text);
    border-color: var(--text-muted);
}

/* ===== Study Setup Layout ===== */

.study-layout {
    display: flex;
    flex-direction: column;
    gap: 20px;
    max-width: 100%;
}

.study-layout .config-card {
    margin-bottom: 0;
}

.forecast-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
}

.forecast-card h2 {
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 20px;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.forecast-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
}

.forecast-item {
    text-align: center;
    padding: 16px;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
}

.forecast-value {
    font-size: 2.2rem;
    font-weight: 800;
    line-height: 1;
    margin-bottom: 6px;
}

.forecast-value.accent {
    color: var(--accent);
}

.forecast-label {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.config-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
}

.config-card h2 {
    font-size: 1.3rem;
    font-weight: 800;
    margin-bottom: 24px;
}

.activity-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    display: flex;
    flex-direction: column;
}

.activity-card h2 {
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 20px;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.activity-list {
    flex: 1;
    overflow-y: auto;
    max-height: 400px;
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.activity-empty {
    color: var(--text-muted);
    font-size: 0.9rem;
    font-style: italic;
    text-align: center;
    margin-top: 40px;
}

.activity-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px 16px;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
}

.activity-date {
    font-size: 0.8rem;
    color: var(--text-muted);
    font-weight: 600;
    width: 60px;
}

.activity-body {
    flex: 1;
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-left: 12px;
}

.activity-system {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text);
}

.activity-score {
    font-size: 0.85rem;
    color: var(--success);
    font-weight: 700;
}

/* ===== Quiz Screen ===== */

.quiz-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 20px;
}

.quiz-progress {
    flex: 1;
    margin-right: 16px;
}

.quiz-progress span {
    font-size: 0.85rem;
    color: var(--text-muted);
    font-weight: 600;
}

.progress-bar {
    width: 100%;
    height: 6px;
    background: var(--border);
    border-radius: 3px;
    margin-top: 8px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary), #a2d2ff);
    border-radius: 3px;
    transition: width 0.35s ease;
}

.quiz-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 32px;
    max-width: 680px;
    margin: 0 auto;
}

.quiz-card.wide {
    max-width: 1000px;
}

.quiz-system {
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--primary);
    margin-bottom: 4px;
}

.quiz-ref {
    font-size: 0.8rem;
    color: var(--text-dim);
    margin-bottom: 16px;
}

.quiz-question {
    font-size: 1.1rem;
    font-weight: 500;
    line-height: 1.7;
    margin-bottom: 24px;
}

.quiz-body {
    display: grid;
    gap: 32px;
}

.quiz-body.has-image {
    grid-template-columns: 1fr 1.1fr;
    align-items: start;
}

#quiz-image-container {
    width: 100%;
    margin-bottom: 24px;
    display: flex;
    justify-content: center;
    align-items: center;
    border-left: 1px solid var(--border);
    padding-left: 24px;
    height: 100%;
}

#quiz-image {
    max-width: 100%;
    max-height: 400px;
    border-radius: var(--radius-sm);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.4);
    border: 1px solid var(--border);
    object-fit: contain;
}

@media (max-width: 800px) {
    .quiz-body.has-image {
        grid-template-columns: 1fr;
    }

    #quiz-image-container {
        border-left: none;
        padding-left: 0;
        border-top: 1px solid var(--border);
        padding-top: 24px;
    }
}

/* Options */

.options {
    display: grid;
    gap: 10px;
}

.option-btn {
    display: block;
    width: 100%;
    text-align: left;
    padding: 14px 18px;
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    color: var(--text);
    font-family: inherit;
    font-size: 0.95rem;
    cursor: pointer;
    transition: all var(--transition);
    line-height: 1.5;
}

.option-btn:hover {
    border-color: var(--primary);
    background: rgba(88, 166, 255, 0.06);
}

.option-btn.selected {
    border-color: var(--primary);
    background: rgba(88, 166, 255, 0.1);
    box-shadow: 0 0 0 1px var(--primary);
}

.option-btn.correct {
    border-color: var(--success);
    background: var(--success-bg);
    box-shadow: 0 0 0 1px var(--success);
}

.option-btn.incorrect {
    border-color: var(--error);
    background: var(--error-bg);
    box-shadow: 0 0 0 1px var(--error);
}

.option-btn.reveal-correct {
    border-color: var(--success);
    background: var(--success-bg);
}

.option-btn.disabled {
    pointer-events: none;
    opacity: 0.7;
}

/* Confidence */

.confidence-row {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-top: 20px;
    flex-wrap: wrap;
}

.confidence-label {
    font-size: 0.8rem;
    color: var(--text-muted);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.conf-btn {
    padding: 6px 14px;
    border: 1px solid var(--border);
    border-radius: 20px;
    background: transparent;
    color: var(--text-muted);
    font-family: inherit;
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition);
}

.conf-btn:hover {
    border-color: var(--text-muted);
    color: var(--text);
}

.conf-btn.active {
    border-color: var(--primary);
    color: var(--primary);
    background: rgba(88, 166, 255, 0.08);
}

/* Feedback */

.feedback {
    margin-top: 16px;
    display: flex;
    align-items: center;
    gap: 10px;
}

.feedback-icon {
    font-size: 1.4rem;
}

.feedback-text {
    font-size: 0.95rem;
    font-weight: 600;
}

.feedback-text.correct {
    color: var(--success);
}

.feedback-text.incorrect {
    color: var(--error);
}

#btn-next {
    margin-top: 16px;
}

/* ===== Summary Screen ===== */

.summary-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 36px;
    text-align: center;
}

.summary-card h2 {
    font-size: 1.3rem;
    font-weight: 800;
    margin-bottom: 20px;
}

.summary-score {
    font-size: 4rem;
    font-weight: 800;
    background: linear-gradient(135deg, var(--primary), #a2d2ff);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    line-height: 1;
    margin-bottom: 8px;
}

.summary-stats {
    display: flex;
    justify-content: center;
    gap: 24px;
    margin-bottom: 28px;
    font-size: 0.9rem;
    color: var(--text-muted);
}

.summary-stats .correct-label {
    color: var(--success);
    font-weight: 600;
}

.summary-stats .incorrect-label {
    color: var(--error);
    font-weight: 600;
}

.summary-systems {
    text-align: left;
    margin-bottom: 24px;
}

.summary-systems h3 {
    font-size: 0.85rem;
    text-transform: uppercase;
    color: var(--text-muted);
    letter-spacing: 0.05em;
    margin-bottom: 12px;
}

.summary-system-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 8px 0;
    border-bottom: 1px solid var(--border);
    font-size: 0.9rem;
}

.summary-system-row:last-child {
    border-bottom: none;
}

.summary-weakest {
    background: var(--error-bg);
    border: 1px solid rgba(248, 81, 73, 0.3);
    border-radius: var(--radius-sm);
    padding: 12px 16px;
    margin-bottom: 24px;
    font-size: 0.9rem;
    color: var(--error);
    text-align: left;
}

/* ===== Progress Dashboard ===== */

.progress-dashboard h2 {
    font-size: 1.3rem;
    font-weight: 800;
    margin-bottom: 24px;
    text-align: center;
}

.progress-rings-row {
    display: flex;
    justify-content: center;
    gap: 40px;
    margin-bottom: 16px;
    flex-wrap: wrap;
}

.progress-ring-wrapper {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
}

.ring-title {
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--text-muted);
}

.cram-ring-fill {
    stroke: var(--success) !important;
}

.cram-projection {
    text-align: center;
    font-size: 0.83rem;
    color: var(--text-muted);
    margin-bottom: 28px;
    padding: 8px 16px;
    background: rgba(188, 140, 85, 0.06);
    border: 1px solid rgba(188, 140, 85, 0.2);
    border-radius: var(--radius-sm);
}

.cram-proj-label {
    font-weight: 700;
    color: var(--accent);
    margin-right: 6px;
}

.progress-ring-container {

    position: relative;
    width: 160px;
    height: 160px;
    margin: 0 auto 28px;
}

.progress-ring {
    width: 100%;
    height: 100%;
    transform: rotate(-90deg);
}

.progress-ring-bg {
    stroke: var(--border);
}

.progress-ring-fill {
    stroke: var(--success);
    stroke-linecap: round;
    transition: stroke-dashoffset 0.8s ease;
}

.progress-ring-label {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    text-align: center;
}

.ring-pct {
    display: block;
    font-size: 2rem;
    font-weight: 800;
    color: var(--text);
    line-height: 1;
}

.ring-sub {
    display: block;
    font-size: 0.75rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-top: 4px;
}

.progress-overview {
    display: grid;
    grid-template-columns: 1fr 1fr 1fr;
    gap: 12px;
    margin-bottom: 32px;
}

.overview-stat {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 18px 12px;
    text-align: center;
}

.overview-value {
    font-size: 1.8rem;
    font-weight: 800;
    line-height: 1;
}

.overview-value.success {
    color: var(--success);
}

.overview-value.accent {
    color: var(--accent);
}

.overview-value.muted {
    color: var(--text-muted);
}

.overview-label {
    font-size: 0.7rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-top: 6px;
}

.section-heading {
    font-size: 0.85rem;
    text-transform: uppercase;
    color: var(--text-muted);
    letter-spacing: 0.05em;
    margin-bottom: 14px;
    font-weight: 600;
}

.progress-systems {
    display: grid;
    gap: 10px;
}

.system-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 16px 18px;
    transition: background var(--transition);
}

.system-card:hover {
    background: var(--bg-card-hover);
}

.system-card-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 10px;
}

.system-card-name {
    font-weight: 600;
    font-size: 0.9rem;
}

.system-card-counts {
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-muted);
}

.system-bar {
    display: flex;
    width: 100%;
    height: 6px;
    background: var(--border);
    border-radius: 3px;
    overflow: hidden;
    margin-bottom: 10px;
}

.system-bar-mastered {
    background: var(--success);
    border-radius: 3px 0 0 3px;
    transition: width 0.4s ease;
}

.system-bar-seen {
    background: var(--primary);
    transition: width 0.4s ease;
}

.system-card-detail {
    display: flex;
    justify-content: space-between;
    font-size: 0.75rem;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    padding-top: 4px;
}

.detail-mastered {
    color: var(--success);
}

.detail-due {
    color: var(--accent);
}

.detail-unseen {
    color: var(--text-muted);
}

.detail-eta {
    color: var(--primary);
    font-weight: 700;
}

.detail-eta.success {
    color: var(--success);
}

/* ===== Informational Section ===== */

.info-section {
    display: flex;
    flex-direction: column;
    gap: 16px;
    margin-top: 0;
    margin-bottom: 40px;
}

.info-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.03);
}

.info-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 16px;
}

.info-icon {
    font-size: 1.5rem;
}

.info-card h3 {
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--text);
    margin: 0;
}

.info-card p {
    font-size: 0.95rem;
    color: var(--text-muted);
    line-height: 1.6;
    margin-bottom: 12px;
}

.info-card p:last-child {
    margin-bottom: 0;
}

.info-card strong {
    color: var(--text);
    font-weight: 600;
}

.info-list {
    list-style: none;
    padding: 0;
    margin: 0 0 16px 0;
}

.info-list li {
    font-size: 0.95rem;
    color: var(--text-muted);
    line-height: 1.6;
    margin-bottom: 8px;
    padding-left: 20px;
    position: relative;
}

.info-list li:before {
    content: "•";
    color: var(--primary);
    position: absolute;
    left: 0;
    top: 0;
    font-weight: bold;
}

.info-card code {
    background: var(--bg);
    padding: 4px 8px;
    border-radius: 4px;
    font-family: monospace;
    font-size: 0.85rem;
    color: var(--accent);
    word-break: break-all;
}

/* ===== Settings Screen ===== */

.settings-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 28px;
}

.settings-card h2 {
    font-size: 1.15rem;
    font-weight: 700;
    margin-bottom: 20px;
}

/* ===== Utility ===== */

.hidden {
    display: none !important;
}

/* ===== About / FSRS Explanation Screen ===== */

.about-container {
    max-width: 800px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 20px;
    padding-bottom: 60px;
}

.about-hero {
    text-align: center;
    padding: 32px 0 8px;
}

.about-hero h2 {
    font-size: 2rem;
    font-weight: 800;
    letter-spacing: -0.03em;
    margin-bottom: 8px;
}

.about-hero p {
    color: var(--text-muted);
    font-size: 1rem;
}

.about-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 28px;
}

.about-card-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 16px;
}

.about-card-header h3 {
    font-size: 1.1rem;
    font-weight: 700;
}

.about-icon {
    font-size: 1.5rem;
    line-height: 1;
}

.about-intro {
    color: var(--text-muted);
    font-size: 0.92rem;
    line-height: 1.7;
    margin-bottom: 20px;
}

.about-note {
    font-size: 0.85rem;
    color: var(--text-muted);
    background: rgba(88, 166, 255, 0.06);
    border-left: 3px solid var(--primary);
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
    padding: 10px 14px;
    margin-top: 16px;
    line-height: 1.6;
}

/* Rating grid */

.about-rating-grid {
    display: flex;
    flex-direction: column;
    gap: 4px;
    border-radius: var(--radius-sm);
    overflow: hidden;
    border: 1px solid var(--border);
}

.rating-row {
    display: grid;
    grid-template-columns: 1fr 1fr 120px 1.5fr;
    gap: 12px;
    align-items: center;
    padding: 10px 16px;
    font-size: 0.88rem;
}

.header-row {
    background: var(--bg);
    font-size: 0.78rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
}

.rating-again {
    background: rgba(248, 81, 73, 0.06);
}

.rating-hard {
    background: rgba(240, 136, 62, 0.06);
}

.rating-good {
    background: rgba(88, 166, 255, 0.06);
}

.rating-easy {
    background: rgba(63, 185, 80, 0.06);
}

/* Badges */

.badge {
    display: inline-block;
    padding: 3px 10px;
    border-radius: 20px;
    font-size: 0.78rem;
    font-weight: 700;
    text-align: center;
}

.badge-again {
    background: var(--error-bg);
    color: var(--error);
    border: 1px solid var(--error);
}

.badge-hard {
    background: rgba(240, 136, 62, 0.12);
    color: var(--accent);
    border: 1px solid var(--accent);
}

.badge-good {
    background: rgba(88, 166, 255, 0.12);
    color: var(--primary);
    border: 1px solid var(--primary);
}

.badge-easy {
    background: var(--success-bg);
    color: var(--success);
    border: 1px solid var(--success);
}

/* Two-col metric cards */

.about-two-col {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
}

.about-metric-card {
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 18px;
}

.about-metric-label {
    font-size: 1rem;
    font-weight: 700;
    color: var(--primary);
    margin-bottom: 8px;
}

.about-metric-desc {
    font-size: 0.88rem;
    color: var(--text-muted);
    line-height: 1.6;
    margin-bottom: 10px;
}

.about-metric-range {
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--text-dim);
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

/* Formula block */

.about-formula {
    font-family: 'Courier New', Courier, monospace;
    font-size: 1.1rem;
    font-weight: 600;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 16px 20px;
    margin: 16px 0;
    color: var(--primary);
    text-align: center;
    letter-spacing: 0.03em;
}

.about-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.about-list li {
    font-size: 0.88rem;
    color: var(--text-muted);
    padding-left: 12px;
    position: relative;
}

.about-list li::before {
    content: '·';
    position: absolute;
    left: 0;
    color: var(--primary);
    font-weight: 700;
}

/* Stability rows */

.about-stability-rows {
    display: flex;
    flex-direction: column;
    gap: 8px;
    margin-bottom: 4px;
}

.stability-row {
    display: flex;
    align-items: center;
    gap: 14px;
    padding: 10px 14px;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 0.88rem;
    color: var(--text-muted);
}

.stability-row .badge {
    flex-shrink: 0;
    min-width: 64px;
}

/* Card lifecycle */

.about-lifecycle {
    display: flex;
    align-items: flex-start;
    gap: 8px;
    flex-wrap: wrap;
}

.lifecycle-step {
    flex: 1;
    min-width: 140px;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 16px;
}

.lifecycle-badge {
    display: inline-block;
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 0.78rem;
    font-weight: 700;
    margin-bottom: 10px;
    background: rgba(88, 166, 255, 0.12);
    color: var(--primary);
    border: 1px solid var(--primary);
}

.lifecycle-badge.review {
    background: var(--success-bg);
    color: var(--success);
    border-color: var(--success);
}

.lifecycle-badge.relearning {
    background: rgba(240, 136, 62, 0.12);
    color: var(--accent);
    border-color: var(--accent);
}

.lifecycle-desc {
    font-size: 0.85rem;
    color: var(--text-muted);
    line-height: 1.6;
}

.lifecycle-arrow {
    font-size: 0.8rem;
    color: var(--text-dim);
    align-self: center;
    white-space: nowrap;
    padding: 0 4px;
}

/* Mastery conditions */

.about-mastery-conditions {
    display: flex;
    align-items: center;
    gap: 16px;
    margin: 20px 0;
    flex-wrap: wrap;
}

.mastery-condition {
    flex: 1;
    min-width: 160px;
    background: var(--success-bg);
    border: 1px solid var(--success);
    border-radius: var(--radius-sm);
    padding: 20px;
    text-align: center;
}

.mastery-value {
    font-size: 1.6rem;
    font-weight: 800;
    color: var(--success);
    margin-bottom: 8px;
}

.mastery-label {
    font-size: 0.82rem;
    color: var(--text-muted);
    line-height: 1.5;
}

.mastery-and {
    font-size: 0.8rem;
    font-weight: 800;
    color: var(--text-dim);
    text-transform: uppercase;
    letter-spacing: 0.08em;
    flex-shrink: 0;
}

/* ===== Responsive ===== */

@media (max-width: 480px) {
    .app {
        padding: 0 14px 40px;
    }

    .quiz-card {
        padding: 22px;
    }

    .summary-score {
        font-size: 3rem;
    }

    .mastery-bar-wrap {
        width: 80px;
    }

    .about-two-col {
        grid-template-columns: 1fr;
    }

    .rating-row {
        grid-template-columns: 1fr 1fr;
        gap: 6px;
    }

    .header-row span:nth-child(3),
    .header-row span:nth-child(4),
    .rating-row span:nth-child(3),
    .rating-row span:nth-child(4) {
        display: none;
    }

    .about-lifecycle {
        flex-direction: column;
    }

    .lifecycle-arrow {
        transform: rotate(90deg);
        align-self: center;
    }
}

/* ===== Flashcard Picker Screen ===== */

.flashcard-picker {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 60px 0 40px;
    gap: 16px;
}

.flashcard-picker h2 {
    font-size: 2rem;
    font-weight: 800;
    letter-spacing: -0.03em;
}

.flashcard-picker-sub {
    color: var(--text-muted);
    font-size: 1rem;
    margin-bottom: 12px;
}

.flashcard-picker-buttons {
    display: flex;
    flex-direction: column;
    gap: 14px;
    width: 100%;
    max-width: 320px;
}

.flashcard-topic-btn {
    font-size: 1.05rem;
    padding: 18px 28px;
    gap: 10px;
}

/* ===== Flashcard Study Screen ===== */

.flashcard-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin: 0 auto 28px;
    max-width: 680px;
    width: 100%;
}

.flashcard-header .back-btn {
    margin-bottom: 0;
}

.flashcard-counter {
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-muted);
    padding: 6px 0;
}

/* --- 3D flip card --- */

.flashcard-scene {
    width: 100%;
    max-width: 680px;
    margin: 0 auto 28px;
    perspective: 1200px;
    cursor: pointer;
    min-height: 300px;
}

.flashcard-inner {
    position: relative;
    width: 100%;
    min-height: 300px;
    transform-style: preserve-3d;
    transition: transform 0.35s cubic-bezier(0.4, 0.0, 0.2, 1);
    border-radius: var(--radius);
    display: grid;
}

.flashcard-inner.flipped {
    transform: rotateX(-180deg);
}

.flashcard-face {
    grid-area: 1 / 1;
    border-radius: var(--radius);
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 40px 36px;
    text-align: center;
    min-height: 300px;
}

/* Front face */
.flashcard-front {
    background: var(--bg-card);
    border: 1px solid var(--border);
}

.flashcard-hint {
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-dim);
    margin-bottom: 20px;
}

.flashcard-front-text {
    font-size: 1.3rem;
    font-weight: 700;
    line-height: 1.5;
    color: var(--text);
    white-space: pre-wrap;
}

/* Back face — slightly different background to feel distinct */
.flashcard-back {
    background: linear-gradient(135deg, #1a2332, #161b22);
    border: 1px solid var(--primary);
    transform: rotateX(180deg);
}

.flashcard-back-text {
    font-size: 0.98rem;
    line-height: 1.8;
    color: var(--text);
    white-space: pre-wrap;
    text-align: left;
    max-width: 100%;
}

/* Hover glow on the scene */
.flashcard-scene:hover .flashcard-inner:not(.flipped) .flashcard-front {
    border-color: var(--primary);
    box-shadow: 0 0 0 1px rgba(88, 166, 255, 0.15), var(--shadow);
}

/* --- Action buttons --- */

.flashcard-actions {
    display: flex;
    gap: 14px;
    max-width: 680px;
    margin: 0 auto;
}

.flashcard-actions .btn-lg {
    flex: 1;
}

@media (max-width: 640px) {
    .flashcard-scene {
        min-height: 260px;
        margin-left: 12px;
        margin-right: 12px;
        width: auto;
    }

    .flashcard-face {
        padding: 28px 20px;
    }

    .flashcard-front-text {
        font-size: 1.1rem;
    }

    .flashcard-back-text {
        font-size: 0.9rem;
    }

    .flashcard-actions {
        flex-direction: column;
        margin-left: 12px;
        margin-right: 12px;
        padding-bottom: 48px;
    }
}

/* ===== PWA / Mobile Polish ===== */

/* Safe area insets for notched iPhones and Android devices */
.header {
    padding-top: max(24px, env(safe-area-inset-top));
}

.app {
    padding-left: max(24px, env(safe-area-inset-left));
    padding-right: max(24px, env(safe-area-inset-right));
    padding-bottom: max(60px, env(safe-area-inset-bottom));
}

/* Prevent scroll bounce in standalone PWA mode */
body {
    overscroll-behavior: none;
}

/* Eliminate 300ms tap delay on interactive elements */
button,
a,
select,
input,
label,
.option-btn,
.flashcard-scene {
    touch-action: manipulation;
}

/* Prevent accidental text selection on tap */
button,
label,
.option-btn,
.size-btn,
.conf-btn,
.menu-btn,
.flashcard-topic-btn,
.back-btn,
.streak-badge {
    -webkit-user-select: none;
    user-select: none;
}

/* ===== Add-to-Home-Screen sheet (non-blocking, centred) ===== */

.install-gate {
    position: fixed;
    inset: 0;
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 16px;
    /* No dim/backdrop and clicks pass through, so the app stays usable behind
       it — only the card is interactive. Centred so iOS Safari's bottom toolbar
       can't clip the install steps. */
    pointer-events: none;
}

.install-gate.hidden {
    display: none;
}

.install-gate-card {
    pointer-events: auto;
    position: relative;
    width: 100%;
    max-width: 420px;
    max-height: calc(100vh - 32px);
    max-height: calc(100dvh - 32px); /* exclude browser chrome on mobile */
    overflow-y: auto;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 22px 20px 20px;
    animation: gatePop 0.25s ease;
}

.install-gate-close {
    position: absolute;
    top: 8px;
    right: 10px;
    background: none;
    border: none;
    color: var(--text-muted);
    font-size: 1.5rem;
    line-height: 1;
    cursor: pointer;
    padding: 2px 8px;
    border-radius: var(--radius-sm);
}

.install-gate-close:hover {
    color: var(--text);
}

.install-gate-head {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 14px;
    padding-right: 28px; /* clear the close button */
}

.install-gate-icon {
    font-size: 1.8rem;
    line-height: 1;
}

.install-gate-card h2 {
    font-size: 1.15rem;
}

.install-gate-benefits {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 9px;
    margin-bottom: 16px;
}

.install-gate-benefits li {
    display: flex;
    align-items: flex-start;
    gap: 9px;
    font-size: 0.85rem;
    color: var(--text);
    line-height: 1.4;
}

.install-gate-benefits li > span:first-child {
    flex-shrink: 0;
}

#install-gate-action .btn {
    width: 100%;
}

.install-manual {
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 12px 14px;
    background: var(--bg-input);
    font-size: 0.88rem;
    color: var(--text);
    line-height: 1.5;
}

.install-steps-list {
    margin: 0;
    padding: 12px 16px 12px 34px;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    background: var(--bg-input);
    font-size: 0.88rem;
    color: var(--text);
    line-height: 1.45;
}

.install-steps-list li {
    margin-bottom: 7px;
}

.install-steps-list li:last-child {
    margin-bottom: 0;
}

.install-step-icon {
    display: inline-block;
    transform: translateY(2px);
}

.install-gate-privacy {
    margin-top: 12px;
    font-size: 0.78rem;
    color: var(--text-muted);
    line-height: 1.45;
    text-align: center;
}

@keyframes gatePop {
    from { opacity: 0; transform: scale(0.96); }
    to   { opacity: 1; transform: scale(1); }
}

/* Update toast */
.update-toast {
    position: fixed;
    bottom: max(24px, env(safe-area-inset-bottom));
    left: 50%;
    transform: translateX(-50%) translateY(0);
    background: var(--success-bg);
    border: 1px solid var(--success);
    color: var(--success);
    border-radius: 999px;
    padding: 10px 20px;
    font-size: 0.875rem;
    font-weight: 500;
    white-space: nowrap;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.4);
    z-index: 2000;
    animation: toastIn 0.3s ease;
    pointer-events: none;
}

.update-toast.hidden {
    display: none;
}

@keyframes toastIn {
    from { opacity: 0; transform: translateX(-50%) translateY(12px); }
    to   { opacity: 1; transform: translateX(-50%) translateY(0); }
}

/* Wrong Answer Review */
.review-container {
    max-width: 720px;
    margin: 0 auto;
    padding: 16px;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.review-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.review-counter {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-muted);
}

.review-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.review-system {
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--text-muted);
}

.review-question {
    font-size: 1.1rem;
    font-weight: 500;
    color: var(--text);
    line-height: 1.5;
    margin: 0;
}

.review-nav {
    display: flex;
    gap: 12px;
}

.review-nav .btn {
    flex: 1;
}

.review-nav .btn:disabled {
    opacity: 0.3;
    pointer-events: none;
}