* { box-sizing: border-box; margin: 0; padding: 0; -webkit-tap-highlight-color: transparent; }

:root {
    --primary: #2563eb; --primary-dark: #1d4ed8; --secondary: #64748b;
    --success: #16a34a; --danger: #dc2626; --warning: #f59e0b;
    --bg: #f1f5f9; --card: #ffffff; --text: #1e293b; --text-light: #64748b;
    --border: #e2e8f0; --radius: 14px;
    --shadow: 0 4px 6px -1px rgba(0,0,0,0.1), 0 2px 4px -1px rgba(0,0,0,0.06);
}

html { font-size: 16px; }

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background: var(--bg); color: var(--text); min-height: 100vh; line-height: 1.5;
    -webkit-font-smoothing: antialiased;
}

.app-container { max-width: 720px; margin: 0 auto; padding: 16px; min-height: 100vh; }

.app-header { text-align: center; margin-bottom: 20px; }
.app-header h1 { font-size: 1.75rem; margin-bottom: 4px; }
.subtitle { color: var(--text-light); font-size: 0.95rem; }

.screen { display: none; animation: fadeIn 0.25s ease-out; }
.screen.active { display: block; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: translateY(0); } }

.card { background: var(--card); border-radius: var(--radius); box-shadow: var(--shadow); padding: 22px; margin-bottom: 16px; }
.card h2, .card h3 { margin-bottom: 16px; font-size: 1.25rem; }

.form-group { margin-bottom: 18px; }
.form-group label { display: block; font-weight: 600; margin-bottom: 6px; font-size: 0.95rem; }

input[type="number"], input[type="text"], select {
    width: 100%; padding: 14px; font-size: 1.1rem; border: 2px solid var(--border);
    border-radius: 10px; background: #fff; color: var(--text); transition: border-color 0.2s;
}
input[type="number"]:focus, input[type="text"]:focus, select:focus { outline: none; border-color: var(--primary); }
input[type="number"]::-webkit-inner-spin-button, input[type="number"]::-webkit-outer-spin-button { opacity: 1; }

.checkbox-group { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
.checkbox { display: flex; align-items: center; gap: 8px; font-weight: 500; cursor: pointer; padding: 6px 0; }
.checkbox input { width: 20px; height: 20px; accent-color: var(--primary); }

.btn {
    display: inline-flex; align-items: center; justify-content: center; gap: 6px;
    padding: 12px 20px; font-size: 1rem; font-weight: 600; border: none; border-radius: 10px;
    cursor: pointer; transition: transform 0.05s, background 0.2s; min-height: 48px;
}
.btn:active { transform: scale(0.98); }
.btn-primary { background: var(--primary); color: white; }
.btn-primary:hover { background: var(--primary-dark); }
.btn-secondary { background: var(--secondary); color: white; }
.btn-secondary:hover { background: #475569; }
.btn-large { width: 100%; padding: 16px; font-size: 1.15rem; }
.btn:disabled { opacity: 0.5; cursor: not-allowed; }

.quiz-header { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; margin-bottom: 12px; }
.stat-box { background: var(--card); border-radius: var(--radius); box-shadow: var(--shadow); padding: 12px; text-align: center; }
.stat-label { display: block; font-size: 0.75rem; color: var(--text-light); text-transform: uppercase; letter-spacing: 0.5px; }
.stat-value { display: block; font-size: 1.25rem; font-weight: 700; margin-top: 2px; }
#timer.low-time { color: var(--danger); animation: pulse 1s infinite; }
@keyframes pulse { 0%,100% { opacity: 1; } 50% { opacity: 0.5; } }

.progress-bar { height: 10px; background: var(--border); border-radius: 5px; overflow: hidden; margin-bottom: 16px; }
.progress-fill { height: 100%; width: 0%; background: var(--primary); transition: width 0.3s ease; }

.questions-container { display: flex; flex-direction: column; gap: 14px; margin-bottom: 16px; }

.question-row {
    background: var(--card);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 16px 18px;
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 12px;
}

.question-number {
    font-weight: 700;
    color: var(--primary);
    min-width: 38px;
    font-size: 1.05rem;
}

.question-text {
    font-size: 1.35rem;
    font-weight: 700;
    flex: 1 1 200px;
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 8px;
}

.answer-field {
    flex: 1 1 160px;
    max-width: 220px;
}

.answer-field input {
    text-align: center;
    font-size: 1.2rem;
    font-weight: 700;
    padding: 12px;
}

.options {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 10px;
    flex: 1 1 220px;
    max-width: 320px;
}

.option {
    display: flex;
    align-items: center;
    justify-content: flex-start;
    gap: 8px;
    padding: 10px 12px;
    border: 2px solid var(--border);
    border-radius: 10px;
    background: #fff;
    color: var(--text);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: border-color 0.2s, background 0.2s, color 0.2s;
    min-height: 44px;
    text-align: left;
}

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

.option.selected {
    background: var(--primary);
    border-color: var(--primary);
    color: #fff;
}

.option-letter {
    font-weight: 700;
}

.question-status {
    font-size: 1.3rem;
    min-width: 28px;
    text-align: center;
}

.fraction { display: inline-flex; flex-direction: column; align-items: center; vertical-align: middle; margin: 0 4px; }
.fraction .num { border-bottom: 2px solid var(--text); padding: 0 4px; }
.fraction .den { padding: 0 4px; }

.pagination { text-align: center; }
.page-actions { display: flex; gap: 12px; margin-bottom: 12px; }
.page-actions .btn { flex: 1; }

.results-card { text-align: center; }
.results-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin-bottom: 20px; }
.result-item { background: var(--bg); border-radius: 10px; padding: 16px; }
.result-label { display: block; font-size: 0.8rem; color: var(--text-light); margin-bottom: 4px; }
.result-value { display: block; font-size: 1.4rem; font-weight: 700; }

.grade-message { padding: 14px; border-radius: 10px; font-weight: 600; margin-bottom: 20px; }
.grade-message.excellent { background: #dcfce7; color: #166534; }
.grade-message.good { background: #dbeafe; color: #1e40af; }
.grade-message.okay { background: #fef3c7; color: #92400e; }
.grade-message.needs-work { background: #fee2e2; color: #991b1b; }

.results-actions { display: flex; gap: 12px; }
.results-actions .btn { flex: 1; }

.screen-inner { display: none; }
.screen-inner.active { display: block; }
.review-list { max-height: 50vh; overflow-y: auto; margin-bottom: 16px; }
.review-item { display: grid; grid-template-columns: 30px 1fr 1fr 1fr; gap: 8px; padding: 10px;
    border-bottom: 1px solid var(--border); align-items: center; font-size: 0.95rem; }
.review-item.correct { background: #f0fdf4; }
.review-item.wrong { background: #fef2f2; }
.review-question { font-weight: 600; }
.review-answer { color: var(--text-light); }
.review-correct { font-weight: 700; color: var(--success); }
.review-status { font-size: 1.1rem; text-align: center; }

.tips ul { padding-left: 18px; }
.tips li { margin-bottom: 8px; font-size: 0.95rem; }
code { background: #e2e8f0; padding: 2px 6px; border-radius: 4px; font-family: ui-monospace, SFMono-Regular, Menlo, monospace; font-size: 0.9em; }

@media (max-width: 480px) {
    .app-container { padding: 10px; }
    .app-header h1 { font-size: 1.5rem; }
    .card { padding: 18px; border-radius: 12px; }
    .checkbox-group { grid-template-columns: 1fr; }
    .quiz-header { gap: 8px; }
    .stat-box { padding: 10px 6px; }
    .stat-value { font-size: 1.05rem; }
    .question-row { padding: 14px; }
    .question-text { font-size: 1.15rem; flex-basis: 100%; }
    .answer-field { max-width: 100%; flex-basis: 100%; }
    .answer-field input { font-size: 1.1rem; }
    .options { flex-basis: 100%; max-width: 100%; }
    .option { font-size: 1rem; }
    .results-grid { grid-template-columns: 1fr; }
    .review-item { grid-template-columns: 24px 1fr; gap: 4px; }
    .review-item > span:nth-child(2) { grid-column: 2; }
    .review-item > span:nth-child(3) { grid-column: 2; }
    .review-item > span:nth-child(4) { grid-column: 2; }
}

@supports (padding-bottom: env(safe-area-inset-bottom)) {
    .app-container { padding-bottom: calc(16px + env(safe-area-inset-bottom)); }
}

@media (prefers-reduced-motion: reduce) {
    * { animation-duration: 0.01ms !important; transition-duration: 0.01ms !important; }
}