:root {
    --bg: #f3f4f6;
    --card: #ffffff;
    --text: #111827;
    --muted: #6b7280;
    --border: #e5e7eb;
    --primary: #4f46e5;
    --primary-dark: #4338ca;
    --success: #16a34a;
    --danger: #dc2626;
    --radius: 18px;
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    background: var(--bg);
    color: var(--text);
    font-family:
        -apple-system,
        BlinkMacSystemFont,
        "Segoe UI",
        Roboto,
        sans-serif;
}

button {
    font: inherit;
}

#app {
    max-width: 680px;
    margin: auto;
    min-height: 100vh;
}


/* HEADER */

.header {
    position: sticky;
    top: 0;
    z-index: 10;

    display: flex;
    align-items: center;
    justify-content: space-between;

    padding: 18px 18px 14px;

    background: rgba(243, 244, 246, .92);
    backdrop-filter: blur(12px);
}

.header h1 {
    margin: 0;
    font-size: 21px;
}

.subtitle {
    color: var(--muted);
    font-size: 12px;
    margin-top: 2px;
}

.icon-btn {
    width: 42px;
    height: 42px;

    border: 1px solid var(--border);
    border-radius: 12px;

    background: var(--card);
    color: var(--text);

    cursor: pointer;
}


/* SCREENS */

.screen {
    padding: 12px 18px 40px;
}

.hidden {
    display: none !important;
}


/* HOME */

.hero {
    text-align: center;
    padding: 30px 10px;
}

.hero-icon {
    font-size: 48px;
}

.hero h2 {
    margin: 14px 0 8px;
    font-size: 27px;
}

.hero p {
    margin: 0 auto;
    max-width: 420px;
    color: var(--muted);
    line-height: 1.5;
}


/* EXERCISES */

.exercise-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
}

.exercise-card {
    text-align: left;

    padding: 18px;

    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);

    cursor: pointer;

    transition:
        transform .15s,
        box-shadow .15s;
}

.exercise-card:active {
    transform: scale(.97);
}

.exercise-card:hover {
    box-shadow: 0 8px 25px rgba(0,0,0,.07);
}

.card-icon {
    display: block;
    font-size: 28px;
    margin-bottom: 15px;
}

.exercise-card strong {
    display: block;
    font-size: 17px;
}

.exercise-card small {
    display: block;
    color: var(--muted);
    margin-top: 5px;
    line-height: 1.35;
}


/* STATS */

.stats-card {
    display: grid;
    grid-template-columns: repeat(3, 1fr);

    margin-top: 18px;

    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
}

.stats-card div {
    padding: 18px 10px;
    text-align: center;
}

.stats-card div + div {
    border-left: 1px solid var(--border);
}

.stats-card span {
    display: block;
    font-size: 12px;
    color: var(--muted);
}

.stats-card strong {
    display: block;
    font-size: 22px;
    margin-top: 5px;
}


/* EXERCISE */

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

    margin-bottom: 18px;
}

.eyebrow {
    font-size: 12px;
    font-weight: 700;
    letter-spacing: .08em;
    color: var(--primary);
}

.exercise-header h2 {
    margin: 4px 0 0;
    font-size: 18px;
}

.score {
    min-width: 48px;
    height: 48px;

    display: flex;
    align-items: center;
    justify-content: center;

    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 14px;

    font-weight: 700;
}


/* QUESTION */

.question-card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);

    padding: 24px;

    text-align: center;
}

.question-text {
    color: var(--muted);
    font-size: 14px;
    margin-bottom: 20px;
}

.question-content {
    font-size: 27px;
    font-weight: 700;
    letter-spacing: .04em;
    line-height: 1.7;
}


/* ANSWERS */

.answers {
    display: grid;
    gap: 10px;
    margin-top: 14px;
}

.answer-btn {
    width: 100%;

    padding: 16px;

    background: var(--card);
    border: 2px solid var(--border);
    border-radius: 14px;

    text-align: left;

    cursor: pointer;

    transition: .15s;
}

.answer-btn:hover {
    border-color: var(--primary);
}

.answer-btn.correct {
    border-color: var(--success);
    background: #f0fdf4;
}

.answer-btn.wrong {
    border-color: var(--danger);
    background: #fef2f2;
}


/* FEEDBACK */

.feedback {
    display: flex;
    gap: 12px;

    margin-top: 14px;
    padding: 16px;

    border-radius: 14px;

    background: var(--card);
    border: 1px solid var(--border);
}

.feedback p {
    margin: 4px 0 0;
    color: var(--muted);
    font-size: 14px;
}


/* BUTTONS */

.primary-btn,
.secondary-btn {
    width: 100%;
    padding: 16px;

    border-radius: 14px;

    cursor: pointer;

    font-weight: 700;
}

.primary-btn {
    margin-top: 16px;

    background: var(--primary);
    color: white;

    border: none;
}

.primary-btn:hover {
    background: var(--primary-dark);
}

.secondary-btn {
    margin-top: 10px;

    background: var(--card);
    color: var(--text);

    border: 1px solid var(--border);
}


/* RESULTS */

.result-card {
    text-align: center;
    padding: 35px 10px 25px;
}

.result-icon {
    font-size: 55px;
}

.result-card h2 {
    margin: 14px 0;
}

.final-score {
    font-size: 52px;
    font-weight: 800;
    color: var(--primary);
}

.result-card p {
    color: var(--muted);
}

.result-stats {
    display: grid;
    grid-template-columns: repeat(3, 1fr);

    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
}

.result-stats div {
    text-align: center;
    padding: 18px 8px;
}

.result-stats strong {
    display: block;
    font-size: 24px;
}

.result-stats span {
    display: block;
    margin-top: 5px;
    color: var(--muted);
    font-size: 11px;
}


/* MOBILE */

@media (max-width: 480px) {

    .exercise-grid {
        grid-template-columns: 1fr;
    }

    .hero {
        padding: 20px 10px 25px;
    }

    .hero h2 {
        font-size: 24px;
    }
}


/* DARK MODE */

@media (prefers-color-scheme: dark) {

    :root {
        --bg: #0f1117;
        --card: #181b23;
        --text: #f3f4f6;
        --muted: #9ca3af;
        --border: #292e39;
    }

    .header {
        background: rgba(15,17,23,.92);
    }

    .answer-btn.correct {
        background: rgba(22,163,74,.12);
    }

    .answer-btn.wrong {
        background: rgba(220,38,38,.12);
    }
}