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

:root {
    --correct: #2d7d46;
    --correct-bg: #e8f5e9;
    --incorrect: #c0392b;
    --incorrect-bg: #fbe9e7;
    --primary: #1a5276;
    --primary-light: #2980b9;
    --bg: #f8f9fa;
    --card-bg: #ffffff;
    --text: #2c3e50;
    --muted: #7f8c8d;
    --border: #dee2e6;
}

body {
    font-family: system-ui, -apple-system, sans-serif;
    max-width: 44rem;
    margin: 0 auto;
    padding: 1rem;
    background: var(--bg);
    color: var(--text);
    line-height: 1.5;
}

/* Navigation */
nav {
    display: flex;
    align-items: center;
    gap: 1.5rem;
    padding: 0.75rem 0;
    margin-bottom: 1.5rem;
    border-bottom: 2px solid var(--primary);
}

.nav-brand {
    font-weight: 800;
    font-size: 1.25rem;
    color: var(--primary);
    text-decoration: none;
    letter-spacing: 1px;
}

.nav-links { display: flex; gap: 1rem; }
.nav-links a {
    text-decoration: none;
    color: var(--muted);
    font-weight: 500;
    padding: 0.25rem 0;
    border-bottom: 2px solid transparent;
    transition: all 0.2s;
}
.nav-links a:hover { color: var(--primary); border-bottom-color: var(--primary); }

/* Headings */
h1 { font-size: 1.5rem; margin-bottom: 1rem; }
h2 { font-size: 1.15rem; margin: 1.5rem 0 0.75rem; color: var(--primary); }

/* Stats Grid */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(8rem, 1fr));
    gap: 0.75rem;
    margin-bottom: 1.5rem;
}

.stat-card {
    background: var(--card-bg);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 1rem;
    text-align: center;
}

.stat-number { font-size: 2rem; font-weight: 700; color: var(--primary); }
.stat-label { font-size: 0.85rem; color: var(--muted); }

/* Progress Bars */
.subelement-list { display: flex; flex-direction: column; gap: 0.5rem; }
.subelement-row {
    display: grid;
    grid-template-columns: 3rem 1fr 4rem;
    align-items: center;
    gap: 0.75rem;
}
.subelement-label { font-weight: 600; font-size: 0.9rem; }
.subelement-count { font-size: 0.85rem; color: var(--muted); text-align: right; }

.progress-bar {
    height: 1.25rem;
    background: #e9ecef;
    border-radius: 4px;
    overflow: hidden;
    display: flex;
}
.progress-fill {
    height: 100%;
    transition: width 0.3s;
}
.progress-fill.mastered { background: var(--correct); }
.progress-fill.learning { background: var(--primary-light); }
.progress-fill:not(.mastered):not(.learning) { background: var(--primary); }

/* Box Distribution */
.box-dist {
    display: flex;
    gap: 0.5rem;
    flex-wrap: wrap;
}
.box-item {
    background: var(--card-bg);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 0.75rem 1rem;
    text-align: center;
    min-width: 5rem;
}
.box-label { font-size: 0.8rem; color: var(--muted); }
.box-count { font-size: 1.5rem; font-weight: 700; }

/* Buttons */
.btn {
    display: inline-block;
    padding: 0.6rem 1.5rem;
    border-radius: 6px;
    text-decoration: none;
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    border: none;
    transition: background 0.2s;
}
.btn-primary { background: var(--primary); color: white; }
.btn-primary:hover { background: var(--primary-light); }
.btn-secondary { background: var(--border); color: var(--text); }
.btn-secondary:hover { background: #ced4da; }
.btn-large { padding: 0.85rem 2.5rem; font-size: 1.1rem; }

.actions { display: flex; gap: 0.75rem; margin: 1.5rem 0; flex-wrap: wrap; }

/* Question Card */
.question-card {
    background: var(--card-bg);
    border: 1px solid var(--border);
    border-radius: 10px;
    padding: 1.5rem;
    margin: 1rem 0;
}
.question-id { font-size: 0.85rem; color: var(--muted); margin-bottom: 0.5rem; font-weight: 600; }
.question-text { font-size: 1.1rem; margin-bottom: 1.25rem; line-height: 1.6; }

/* Answer Buttons (Study Mode) */
.answers { display: flex; flex-direction: column; gap: 0.5rem; }
.answer-btn {
    display: flex;
    align-items: flex-start;
    gap: 0.75rem;
    width: 100%;
    padding: 0.85rem 1rem;
    border: 2px solid var(--border);
    border-radius: 8px;
    cursor: pointer;
    text-align: left;
    font-size: 1rem;
    background: var(--card-bg);
    transition: all 0.15s;
    line-height: 1.4;
}
.answer-btn:hover:not(.disabled) { border-color: var(--primary); background: #f0f4f8; }
.answer-btn.correct { border-color: var(--correct); background: var(--correct-bg); }
.answer-btn.incorrect { border-color: var(--incorrect); background: var(--incorrect-bg); }
.answer-btn.disabled { cursor: default; opacity: 0.7; }
.answer-btn.correct-answer { border-color: var(--correct); background: var(--correct-bg); opacity: 1; }

.answer-letter {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 1.75rem;
    height: 1.75rem;
    border-radius: 50%;
    background: #e9ecef;
    font-weight: 700;
    font-size: 0.85rem;
    flex-shrink: 0;
}

/* Answer Options (Exam Mode) */
.answer-option {
    display: flex;
    align-items: flex-start;
    gap: 0.75rem;
    padding: 0.85rem 1rem;
    border: 2px solid var(--border);
    border-radius: 8px;
    cursor: pointer;
    margin-bottom: 0.5rem;
    transition: border-color 0.15s;
    line-height: 1.4;
}
.answer-option:hover { border-color: var(--primary); }
.answer-option input[type="radio"] { margin-top: 0.25rem; }

/* Study Header */
.study-header {
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    flex-wrap: wrap;
    gap: 0.5rem;
}
.study-info {
    display: flex;
    gap: 1rem;
    font-size: 0.9rem;
    color: var(--muted);
    align-items: center;
}
.new-badge {
    background: var(--primary-light);
    color: white;
    padding: 0.15rem 0.5rem;
    border-radius: 4px;
    font-size: 0.75rem;
    font-weight: 700;
}
.toggle-new {
    font-size: 0.8rem;
    color: var(--primary-light);
    text-decoration: none;
}
.toggle-new:hover { text-decoration: underline; }

/* Result feedback */
.result {
    margin-top: 1.25rem;
    padding: 1rem;
    border-radius: 8px;
    background: #f8f9fa;
}
.result.correct-result { background: var(--correct-bg); }
.result.incorrect-result { background: var(--incorrect-bg); }
#result-text { font-weight: 600; font-size: 1.05rem; margin-bottom: 0.5rem; }
#result-box { font-size: 0.9rem; color: var(--muted); margin-bottom: 1rem; }

/* Exam */
.exam-intro { text-align: center; padding: 2rem 0; }
.exam-intro ul { list-style: none; margin: 1.5rem 0; }
.exam-intro li { margin: 0.5rem 0; font-size: 1.05rem; }

.exam-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 0.5rem;
}
.exam-timer { font-size: 1.25rem; font-weight: 700; font-variant-numeric: tabular-nums; }
.exam-progress { margin-top: 1rem; }

/* Exam Results */
.result-summary {
    text-align: center;
    padding: 2rem;
    border-radius: 10px;
    margin: 1rem 0;
}
.result-summary.pass { background: var(--correct-bg); border: 2px solid var(--correct); }
.result-summary.fail { background: var(--incorrect-bg); border: 2px solid var(--incorrect); }
.result-score { font-size: 3rem; font-weight: 800; }
.result-percent { font-size: 1.25rem; color: var(--muted); }
.result-verdict { font-size: 1.5rem; font-weight: 700; margin: 0.5rem 0; }
.result-summary.pass .result-verdict { color: var(--correct); }
.result-summary.fail .result-verdict { color: var(--incorrect); }

.question-review { display: flex; flex-direction: column; gap: 0.5rem; }
.review-item {
    padding: 0.75rem;
    border-radius: 6px;
    font-size: 0.9rem;
    border-left: 4px solid var(--border);
}
.review-item.correct { border-left-color: var(--correct); background: var(--correct-bg); }
.review-item.incorrect { border-left-color: var(--incorrect); background: var(--incorrect-bg); }

.pass { color: var(--correct); font-weight: 700; }
.fail { color: var(--incorrect); font-weight: 700; }
.skip { color: var(--muted); font-weight: 600; }

/* Session Tables */
.session-table { width: 100%; border-collapse: collapse; font-size: 0.9rem; }
.session-table th { text-align: left; padding: 0.5rem; border-bottom: 2px solid var(--border); color: var(--muted); font-weight: 600; }
.session-table td { padding: 0.5rem; border-bottom: 1px solid var(--border); }

/* Mobile adjustments */
@media (max-width: 600px) {
    body { padding: 0.5rem; }
    nav { flex-direction: column; align-items: flex-start; gap: 0.5rem; }
    .stats-grid { grid-template-columns: repeat(2, 1fr); }
    .study-header { flex-direction: column; }
    .exam-header { flex-direction: column; gap: 0.5rem; }
}