:root {
    --primary: #2563eb;
    --primary-hover: #1d4ed8;
    --success: #10b981;
    --success-hover: #059669;
    --danger: #ef4444;
    --background: #f3f4f6;
    --surface: #ffffff;
    --text-main: #1f2937;
    --text-muted: #6b7280;
    --border: #e5e7eb;
    --radius: 12px;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
}

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--background);
    color: var(--text-main);
    margin: 0;
    padding: 40px 20px;
    line-height: 1.6;
}

.container {
    max-width: 900px;
    margin: auto;
}

.header {
    text-align: center;
    margin-bottom: 40px;
}

.header h1 {
    font-weight: 700;
    color: var(--primary);
    font-size: 2.5rem;
    margin-bottom: 10px;
}

.header p {
    color: var(--text-muted);
    font-size: 1.1rem;
}

.card {
    background: var(--surface);
    padding: 30px;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-bottom: 24px;
    border: 1px solid var(--border);
}

/* Nút bấn & Inputs */
button {
    padding: 12px 24px;
    border: none;
    border-radius: 8px;
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.2s ease;
}

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

.btn-success { background: var(--success); color: white; width: 100%; margin-top: 15px; }
.btn-success:hover { background: var(--success-hover); }

.btn-outline { background: transparent; border: 2px solid var(--border); color: var(--text-muted); }
.btn-outline.active { border-color: var(--primary); color: var(--primary); background: #eff6ff; }

input[type="text"], input[type="password"], input[type="file"], textarea {
    width: 100%;
    padding: 12px;
    margin-top: 8px;
    border: 1px solid var(--border);
    border-radius: 8px;
    font-family: inherit;
    font-size: 1rem;
    box-sizing: border-box;
    transition: border-color 0.2s;
}

input[type="text"]:focus, textarea:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

/* Chế độ xem & Bố cục */
.mode-switch {
    display: flex;
    justify-content: center;
    gap: 12px;
    margin-bottom: 30px;
    display: none; /* Ánh xạ từ JS cũ */
}

.question-box {
    border-left: 6px solid var(--primary);
    transition: transform 0.2s ease;
}

.question-box:hover {
    transform: translateX(4px);
}

.question-title {
    font-size: 1.15rem;
    font-weight: 600;
    margin-bottom: 15px;
}

/* Đáp án */
.option-wrapper {
    margin: 10px 0;
    display: flex;
    align-items: center;
}

.option-practice {
    display: flex;
    align-items: center;
    padding: 12px 16px;
    border: 1px solid var(--border);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s;
    background: #f9fafb;
    margin-bottom: 8px;
}

.option-practice:hover {
    background: #f3f4f6;
    border-color: #d1d5db;
}

.option-practice input[type="radio"] {
    display: none;
}

/* Khối hiển thị A B C D (Tách riêng biệt) */
.opt-badge {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 32px;
    height: 32px;
    background-color: #e5e7eb;
    color: var(--text-main);
    font-weight: 700;
    border-radius: 8px;
    margin-right: 12px;
    flex-shrink: 0;
    transition: all 0.2s ease;
}

.option-practice:hover .opt-badge {
    background-color: #d1d5db;
}

.option-practice.selected {
    border-color: var(--primary);
    background-color: #eff6ff;
}

.option-practice.selected .opt-badge {
    background-color: var(--primary);
    color: white;
}

.correct .opt-badge {
    background-color: #10b981 !important;
    color: white !important;
    border: none;
}

.incorrect .opt-badge {
    background-color: #ef4444 !important;
    color: white !important;
    border: none;
}

.opt-text {
    flex-grow: 1;
    line-height: 1.5;
}

/* Trạng thái chấm điểm */
.correct { background-color: #d1fae5 !important; border-color: #34d399 !important; color: #065f46; font-weight: 600; }
.incorrect { background-color: #fee2e2 !important; border-color: #f87171 !important; color: #991b1b; text-decoration: line-through; }

#score-board {
    display: none;
    text-align: center;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary);
    background: #eff6ff;
    padding: 20px;
    border-radius: var(--radius);
    margin-bottom: 24px;
    border: 1px dashed var(--primary);
}

.navbar {
    display: flex; justify-content: space-between; align-items: center; 
    background: var(--surface); padding: 15px 20px; border-radius: var(--radius); 
    box-shadow: var(--shadow); margin-bottom: 24px; border: 1px solid var(--border);
}

@keyframes pulse-red {
    0% { background-color: var(--danger); }
    50% { background-color: #991b1b; }
    100% { background-color: var(--danger); }
}

.upload-section { text-align: center; }
.upload-section p { margin-bottom: 15px; font-weight: 600; }

/* --- CHẾ ĐỘ TỐI GIẢN (MINIMAL MODE) --- */
body.minimal-mode .header,
body.minimal-mode .navbar,
body.minimal-mode #studentDashboard,
body.minimal-mode #uploadBox,
body.minimal-mode #teacherDashboard {
    display: none !important;
}

body.minimal-mode #exitMinimalBtn {
    display: inline-block !important;
}

body.minimal-mode {
    padding: 10px;
    height: 100dvh;
    overflow: hidden; /* Cấm cuộn toàn trang */
    display: flex;
    flex-direction: column;
    box-sizing: border-box;
}

body.minimal-mode #mainAppContainer {
    display: flex;
    flex-direction: column;
    flex-grow: 1;
    overflow: hidden;
}

body.minimal-mode #quiz-container {
    flex-grow: 1;
    overflow-y: auto; /* Chỉ cuộn vùng nội dung câu hỏi nếu quá dài */
    padding: 5px;
    padding-bottom: 60px; /* Tăng khoảng đệm để nút không sát mép màn hình */
    scrollbar-width: thin;
}

/* Thu gọn Header để tiết kiệm diện tích */
body.minimal-mode #studentHeader {
    padding: 10px 15px;
    margin-bottom: 10px;
    flex-shrink: 0;
}

body.minimal-mode .quiz-title-text {
    font-size: 1.1rem;
    margin-bottom: 5px;
    padding: 0 70px; /* Tránh đè nút thoát */
}

body.minimal-mode #studentHeader div {
    font-size: 0.85rem;
    gap: 12px !important;
}

body.minimal-mode #exitMinimalBtn {
    padding: 6px 12px;
    font-size: 0.85rem;
    top: 10px;
    left: 10px;
}

body.minimal-mode .question-box {
    padding: 20px 25px;
    font-size: 1.1rem;
    border-left: 5px solid var(--primary);
    margin-bottom: 15px;
}

body.minimal-mode .question-title {
    font-size: 1.15rem;
    margin-bottom: 15px;
    line-height: 1.5;
}

body.minimal-mode .option-practice {
    padding: 10px 15px;
    font-size: 1rem;
    margin-bottom: 10px;
}

body.minimal-mode .opt-badge {
    width: 30px;
    height: 30px;
    font-size: 1rem;
    margin-right: 12px;
}

body.minimal-mode #submitBtn {
    flex-shrink: 0;
    margin: 10px 0 0 0;
    border-radius: 12px;
    padding: 15px;
    font-size: 1.1rem;
    z-index: 10;
}

.quiz-title-text { font-size: 1.8rem; }

/* Responsive cho điện thoại */
@media (max-width: 600px) {
    body { padding: 15px 10px; }
    .header h1 { font-size: 1.8rem; }
    .header p { font-size: 1rem; }
    .mode-switch { flex-wrap: wrap; gap: 8px; }
    .mode-switch button { flex: 1 1 calc(50% - 8px); padding: 10px; font-size: 0.9rem; }
    #btnShuffle { flex: 1 1 100%; }
    .card { padding: 15px; }
    .option-wrapper { align-items: center; }
    .option-wrapper input[type="radio"] { flex-shrink: 0; }
    .option-wrapper input[type="text"] { flex-grow: 1; margin-left: 8px; }
    .option-practice { padding: 10px; font-size: 0.95rem; }
    
    body.minimal-mode .question-box { padding: 15px; }
    body.minimal-mode .question-title { font-size: 1.1rem; }
    body.minimal-mode .option-practice { font-size: 0.95rem; }
    body.minimal-mode #exitMinimalBtn { position: absolute !important; top: 10px !important; left: 10px !important; margin-bottom: 0; width: auto; }
    body.minimal-mode .quiz-title-text { font-size: 1.05rem; padding: 0 50px; }
}

/* Khi hoàn thành bài, cho phép cuộn toàn trang */
body.minimal-mode.quiz-completed {
    height: auto;
    overflow: auto;
    display: block;
}

body.minimal-mode.quiz-completed #mainAppContainer {
    display: block;
    overflow: visible;
}

body.minimal-mode.quiz-completed #quiz-container {
    overflow-y: visible;
    padding-bottom: 20px;
}