:root {
    --primary: #ffffff;
    --secondary: #f0f4f8;
    --accent: #e63946;
    --accent-light: #ff4d5a;
    --accent-dark: #c1121f;
    --success: #06d6a0;
    --success-dark: #05a87e;
    --warning: #f77f00;
    --info: #118ab2;
    --text: #1d3557;
    --text-muted: #457b9d;
    --bg: #f8f9fc;
    --card: #ffffff;
    --border: #dde4ee;
    --correct: #06d6a0;
    --incorrect: #e63946;
    --shadow: 0 2px 12px rgba(29,53,87,0.08);
    --shadow-lg: 0 8px 30px rgba(29,53,87,0.12);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg);
    color: var(--text);
    min-height: 100vh;
}

.screen { display: none; min-height: 100vh; }
.screen.active { display: flex; }

/* Landing Screen */
#screen-landing {
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, #f8f9fc 0%, #e8edf5 50%, #dbe2ef 100%);
}

.container { max-width: 700px; width: 100%; padding: 40px 20px; text-align: center; }

.logo { font-size: 2rem; font-weight: 800; margin-bottom: 20px; color: var(--accent); }
.logo-small { font-size: 1rem; font-weight: 700; color: var(--accent); }

h1 { font-size: 2.4rem; font-weight: 800; margin-bottom: 12px; line-height: 1.2; color: var(--text); }
.subtitle { color: var(--text-muted); font-size: 1.1rem; margin-bottom: 40px; }

.code-entry {
    background: var(--card); border-radius: 16px; padding: 32px; margin-bottom: 40px;
    border: 1px solid var(--border); box-shadow: var(--shadow-lg);
}
.code-entry label { display: block; font-size: 0.9rem; color: var(--text-muted); margin-bottom: 12px; }
.code-entry input {
    width: 100%; padding: 16px; font-size: 1.3rem; text-align: center;
    background: var(--secondary); border: 2px solid var(--border); border-radius: 12px;
    color: var(--text); font-family: 'Courier New', monospace; letter-spacing: 4px;
    margin-bottom: 16px; outline: none; transition: border-color 0.3s;
}
.code-entry input:focus { border-color: var(--accent); }
.code-entry button {
    width: 100%; padding: 16px; font-size: 1.1rem; font-weight: 700;
    background: var(--accent); color: white; border: none; border-radius: 12px;
    cursor: pointer; transition: all 0.3s;
}
.code-entry button:hover { background: var(--accent-light); transform: translateY(-2px); box-shadow: 0 4px 15px rgba(230,57,70,0.3); }
.hint { color: var(--text-muted); font-size: 0.85rem; margin-top: 12px; }
.exam-select { margin-bottom: 16px; }
.exam-select label { display: block; font-size: 0.9rem; color: var(--text-muted); margin-bottom: 8px; }
.exam-select select {
    width: 100%; padding: 12px; font-size: 1rem; background: var(--secondary);
    border: 2px solid var(--border); border-radius: 12px; color: var(--text);
    outline: none; cursor: pointer; appearance: none;
    -webkit-appearance: none; -moz-appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24' fill='none' stroke='%23457b9d' stroke-width='2'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
    background-repeat: no-repeat; background-position: right 12px center;
}
.exam-select select:focus { border-color: var(--accent); }

.features { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }
.feature {
    background: var(--card); border-radius: 12px; padding: 20px;
    border: 1px solid var(--border); font-size: 0.9rem; line-height: 1.5;
    box-shadow: var(--shadow); color: var(--text);
}
.feature strong { color: var(--text); }

/* Exam Screen */
#screen-exam { flex-direction: column; }

.exam-header {
    display: flex; justify-content: space-between; align-items: center;
    padding: 12px 20px; background: var(--card); border-bottom: 2px solid var(--border);
    position: sticky; top: 0; z-index: 100; box-shadow: 0 2px 8px rgba(0,0,0,0.06);
}
.exam-header-left { display: flex; align-items: center; gap: 20px; }
.exam-header-right { display: flex; align-items: center; gap: 16px; }

.timer {
    font-size: 1.4rem; font-weight: 700; font-family: 'Courier New', monospace;
    color: var(--info); padding: 8px 16px; background: #e8f4f8;
    border-radius: 8px; border: 2px solid #b8dce8;
}
.timer.warning { color: var(--warning); background: #fff3e0; border-color: #ffd699; }
.timer.danger { color: var(--accent); background: #ffeaec; border-color: #ffb3b8; animation: pulse 1s infinite; }

@keyframes pulse { 0%,100% { opacity: 1; } 50% { opacity: 0.6; } }

.btn-danger {
    padding: 10px 20px; background: var(--accent); color: white;
    border: none; border-radius: 8px; font-weight: 600; cursor: pointer;
    font-size: 0.9rem; transition: all 0.3s;
}
.btn-danger:hover { background: var(--accent-dark); }

.exam-body { display: flex; flex: 1; overflow: hidden; background: var(--bg); }

.question-nav {
    width: 80px; min-width: 80px; background: var(--card); padding: 12px 8px;
    overflow-y: auto; display: grid; grid-template-columns: repeat(2, 1fr);
    gap: 4px; align-content: start; border-right: 2px solid var(--border);
}
.q-nav-btn {
    width: 32px; height: 32px; border: 2px solid var(--border); border-radius: 6px;
    background: var(--bg); color: var(--text-muted); font-size: 0.75rem; font-weight: 600;
    cursor: pointer; display: flex; align-items: center; justify-content: center;
    transition: all 0.2s;
}
.q-nav-btn:hover { border-color: var(--accent); background: #ffeaec; }
.q-nav-btn.active { background: var(--accent); color: white; border-color: var(--accent); }
.q-nav-btn.answered { background: #e8f8f0; color: var(--success-dark); border-color: var(--success); }
.q-nav-btn.flagged { border-color: var(--warning); box-shadow: 0 0 0 2px rgba(247,127,0,0.3); }

.question-area { flex: 1; padding: 40px; max-width: 800px; margin: 0 auto; overflow-y: auto; }
.question-badge {
    display: inline-block; padding: 4px 12px; border-radius: 20px; font-size: 0.8rem;
    background: #e8f4f8; color: var(--info); margin-bottom: 16px; font-weight: 600;
    border: 1px solid #b8dce8;
}
.question-area h2 { font-size: 1.3rem; font-weight: 600; line-height: 1.6; margin-bottom: 24px; color: var(--text); }

.options { display: flex; flex-direction: column; gap: 12px; }
.option-btn {
    padding: 16px 20px; background: var(--card); border: 2px solid var(--border);
    border-radius: 12px; cursor: pointer; text-align: left; font-size: 1rem;
    color: var(--text); transition: all 0.2s; line-height: 1.5; box-shadow: var(--shadow);
}
.option-btn:hover { border-color: var(--info); background: #f0f7fa; transform: translateX(4px); }
.option-btn.selected { border-color: var(--accent); background: #ffeaec; font-weight: 600; }

.question-controls {
    display: flex; justify-content: space-between; margin-top: 32px; padding-top: 20px;
    border-top: 2px solid var(--border);
}
.question-controls button {
    padding: 12px 24px; border: 2px solid var(--border); border-radius: 8px;
    background: var(--card); color: var(--text); cursor: pointer; font-size: 0.95rem;
    font-weight: 600; transition: all 0.2s; box-shadow: var(--shadow);
}
.question-controls button:hover { border-color: var(--info); background: #f0f7fa; }
#btn-flag.flagged { background: #fff3e0; border-color: var(--warning); color: var(--warning); }

/* Results Screen */
#screen-results {
    align-items: center; justify-content: center;
    background: linear-gradient(135deg, #f8f9fc 0%, #e8edf5 100%);
}
.results-container { max-width: 600px; }

.result-badge {
    display: inline-block; padding: 8px 24px; border-radius: 30px; font-size: 1.1rem;
    font-weight: 700; margin-bottom: 12px;
}
.result-badge.pass { background: #e6faf2; color: var(--success-dark); border: 2px solid var(--success); }
.result-badge.fail { background: #ffeaec; color: var(--accent); border: 2px solid var(--accent); }

#result-title { font-size: 2rem; margin-bottom: 24px; color: var(--text); }

.score-display { display: flex; justify-content: center; margin: 24px 0; }
.score-circle {
    width: 160px; height: 160px; border-radius: 50%; display: flex;
    align-items: center; justify-content: center; font-size: 2.5rem; font-weight: 800;
}
.score-circle.pass { background: #e6faf2; border: 4px solid var(--success); color: var(--success-dark); }
.score-circle.fail { background: #ffeaec; border: 4px solid var(--accent); color: var(--accent); }

.stats-grid {
    display: grid; grid-template-columns: repeat(2, 1fr); gap: 12px; margin: 24px 0;
}
.stat-card {
    background: var(--card); border-radius: 12px; padding: 16px; text-align: center;
    border: 1px solid var(--border); box-shadow: var(--shadow);
}
.stat-card .stat-value { font-size: 1.8rem; font-weight: 700; color: var(--text); }
.stat-card .stat-label { font-size: 0.85rem; color: var(--text-muted); margin-top: 4px; }

.result-actions { display: flex; gap: 12px; justify-content: center; margin-top: 24px; }
.result-actions button {
    padding: 14px 28px; border-radius: 12px; font-size: 1rem; font-weight: 600;
    cursor: pointer; border: 2px solid var(--border); background: var(--card);
    color: var(--text); transition: all 0.3s; box-shadow: var(--shadow);
}
.result-actions button:hover { border-color: var(--accent); transform: translateY(-2px); box-shadow: var(--shadow-lg); }

/* Review Screen */
#screen-review { flex-direction: column; background: var(--bg); }
.review-header {
    display: flex; justify-content: space-between; align-items: center;
    padding: 12px 20px; background: var(--card); border-bottom: 2px solid var(--border);
    position: sticky; top: 0; z-index: 100; box-shadow: 0 2px 8px rgba(0,0,0,0.06);
}
.review-header select, .review-header button {
    padding: 8px 16px; background: var(--card); border: 2px solid var(--border);
    border-radius: 8px; color: var(--text); cursor: pointer; font-size: 0.9rem;
    margin-left: 8px; font-weight: 600;
}
.review-header select:hover, .review-header button:hover { border-color: var(--info); }
.review-body { padding: 20px; max-width: 800px; margin: 0 auto; width: 100%; }

.review-card {
    background: var(--card); border-radius: 12px; padding: 24px; margin-bottom: 16px;
    border-left: 4px solid var(--border); box-shadow: var(--shadow);
}
.review-card.correct { border-left-color: var(--correct); }
.review-card.incorrect { border-left-color: var(--incorrect); }
.review-card .q-number { color: var(--text-muted); font-size: 0.85rem; margin-bottom: 8px; font-weight: 600; }
.review-card .q-text { font-size: 1.05rem; font-weight: 600; margin-bottom: 16px; line-height: 1.5; color: var(--text); }
.review-option { padding: 8px 12px; margin: 4px 0; border-radius: 8px; font-size: 0.95rem; }
.review-option.correct-answer { background: #e6faf2; color: var(--success-dark); font-weight: 600; }
.review-option.user-wrong { background: #ffeaec; color: var(--accent); text-decoration: line-through; }
.review-option.user-correct { background: #e6faf2; color: var(--success-dark); font-weight: 600; }
.review-explanation {
    margin-top: 12px; padding: 12px; background: var(--secondary); border-radius: 8px;
    font-size: 0.9rem; line-height: 1.6; color: var(--text-muted);
    border: 1px solid var(--border);
}
.review-explanation strong { color: var(--accent); }

/* Modal */
.modal-overlay {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(29,53,87,0.5); display: flex; align-items: center;
    justify-content: center; z-index: 1000; backdrop-filter: blur(4px);
}
.modal {
    background: var(--card); border-radius: 16px; padding: 32px; max-width: 400px;
    width: 90%; text-align: center; border: 1px solid var(--border); box-shadow: var(--shadow-lg);
}
.modal h3 { margin-bottom: 12px; color: var(--text); }
.modal p { color: var(--text-muted); margin-bottom: 24px; }
.modal-actions { display: flex; gap: 12px; justify-content: center; }
.modal-actions button {
    padding: 12px 24px; border-radius: 8px; font-weight: 600; cursor: pointer;
    border: 2px solid var(--border); background: var(--card); color: var(--text);
}
.modal-actions .btn-confirm { background: var(--accent); border-color: var(--accent); color: white; }

/* Responsive */
@media (max-width: 768px) {
    h1 { font-size: 1.6rem; }
    .features { grid-template-columns: 1fr; }
    .question-nav { width: 50px; min-width: 50px; grid-template-columns: 1fr; }
    .question-area { padding: 20px; }
    .question-area h2 { font-size: 1.1rem; }
    .exam-header { flex-wrap: wrap; gap: 8px; }
    .stats-grid { grid-template-columns: 1fr 1fr; }
    .result-actions { flex-direction: column; }
    .result-actions button { width: 100%; }
}