:root {
    --primary: #6366f1;
    --primary-dark: #4f46e5;
    --bg-gradient: linear-gradient(135deg, #e0e7ff 0%, #f3e8ff 100%);
    --white: #FFFFFF;
    --text: #1F2937;
    --text-light: #6B7280;
    --success: #10B981;
    --error: #EF4444;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
}

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

body {
    font-family: 'Inter', sans-serif;
    background: var(--bg-gradient);
    color: var(--text);
    height: 100vh;
    overflow: hidden; /* Ngăn cuộn trang chính */
    display: flex;
    justify-content: center;
}

.app-container {
    width: 100%; max-width: 600px; height: 100%;
    background: var(--white); 
    display: flex; flex-direction: column;
    position: relative;
    box-shadow: var(--shadow-lg);
    overflow-x: hidden; /* Ngăn kéo ngang */
}

@media (min-width: 600px) {
    .app-container { height: 95vh; margin-top: 2.5vh; border-radius: 24px; }
}

.screen { flex: 1; display: flex; flex-direction: column; height: 100%; overflow: hidden; }
.hidden { display: none !important; }

/* --- MÀN HÌNH CHỜ --- */
#loading-screen { 
    justify-content: center; align-items: center; padding: 30px; 
}
.welcome-card { width: 100%; text-align: center; }

.app-title { font-size: 2.2rem; font-weight: 800; margin-bottom: 8px; color: #111827; }
#status-text { margin-bottom: 40px; color: var(--text-light); }

.toggle-wrapper { 
    display: inline-flex; align-items: center; justify-content: center; 
    margin-bottom: 40px;
}
.toggle-switch { position: relative; width: 44px; height: 24px; margin-right: 12px; }
.toggle-switch input { opacity: 0; width: 0; height: 0; }
.slider { position: absolute; cursor: pointer; top: 0; left: 0; right: 0; bottom: 0; background-color: #cbd5e1; border-radius: 34px; transition: .3s; }
.slider:before { position: absolute; content: ""; height: 18px; width: 18px; left: 3px; bottom: 3px; background-color: white; border-radius: 50%; transition: .3s; box-shadow: 0 1px 2px rgba(0,0,0,0.2); }
input:checked + .slider { background-color: var(--primary); }
input:checked + .slider:before { transform: translateX(20px); }
.label-text { font-weight: 600; font-size: 1rem; color: #4b5563; }

.mode-buttons { display: flex; flex-direction: column; gap: 16px; }
.btn-start { 
    border: none; padding: 18px; border-radius: 12px; 
    font-size: 1.1rem; font-weight: 600; cursor: pointer; width: 100%; 
    transition: 0.2s;
}
.btn-start:active { transform: scale(0.98); }

.btn-primary { 
    background: var(--primary); color: white; 
    box-shadow: 0 4px 6px -1px rgba(99, 102, 241, 0.4); 
}
.btn-primary:hover { background: var(--primary-dark); }
.btn-secondary { background: white; color: var(--text); border: 2px solid #e5e7eb; }
.btn-outline { background: transparent; color: var(--text-light); border: 2px solid #e5e7eb; }

/* --- HEADER --- */
.sticky-header {
    background: rgba(255, 255, 255, 0.98);
    border-bottom: 1px solid #f3f4f6;
    padding: 12px 16px;
    z-index: 50;
}

.header-info {
    display: flex; justify-content: space-between; align-items: center;
    margin-bottom: 10px; font-weight: 700; font-size: 0.95rem; color: #374151;
}
.info-item.center { color: var(--primary); font-size: 1.1rem; }
.info-item.right { text-align: right; }

#btn-home-nav {
    background: #f3f4f6; border: none; padding: 8px 16px;
    border-radius: 8px; font-weight: 600; font-size: 0.85rem;
    color: #4b5563; cursor: pointer;
}

.progress-bg { height: 6px; background: #f3f4f6; border-radius: 10px; overflow: hidden; }
#progress-bar { height: 100%; background: var(--success); width: 0%; transition: width 0.3s ease; }

/* --- CÂU HỎI (QUAN TRỌNG: FIX LỖI KÉO NGANG) --- */
.quiz-scroll-area { 
    flex: 1; 
    overflow-y: auto; 
    overflow-x: hidden; /* Chặn kéo ngang */
    padding: 16px; 
    background: #f9fafb; 
}

.question-block {
    background: white; border-radius: 16px; padding: 20px;
    margin-bottom: 20px; box-shadow: var(--shadow-sm);
    width: 100%; /* Đảm bảo không vượt quá khung */
}

/* Xử lý xuống dòng cho text dài */
.question-text { 
    font-weight: 700; font-size: 1.1rem; margin-bottom: 20px; 
    line-height: 1.5; color: #111827; 
    word-wrap: break-word; 
    overflow-wrap: break-word; /* Bắt buộc xuống dòng nếu từ quá dài */
}

.option-item {
    display: flex; align-items: flex-start;
    padding: 14px; margin-bottom: 12px;
    border: 2px solid #f3f4f6; border-radius: 12px;
    cursor: pointer; background: white;
}
.option-item input { margin-right: 12px; margin-top: 4px; width: 20px; height: 20px; flex-shrink: 0; accent-color: var(--primary); }

.option-item span { 
    line-height: 1.5; font-size: 1rem; color: #374151; 
    word-break: break-word; /* Đảm bảo đáp án dài tự xuống dòng */
}

/* Màu sắc trạng thái */
.option-item.wrong { background-color: #FEF2F2; border-color: var(--error); color: #991B1B; }
.option-item.correct { background-color: #ECFDF5; border-color: var(--success); color: #065F46; font-weight: 600; }

.question-block.completed .option-item { pointer-events: none; opacity: 0.6; }
.question-block.completed .option-item.correct { opacity: 1; border-color: var(--success); }
.question-block.completed .option-item.wrong { opacity: 1; }

/* --- KẾT QUẢ --- */
#result-screen { justify-content: center; align-items: center; background: white; padding: 20px; }
.result-card { text-align: center; width: 100%; }
.result-title { font-size: 2rem; font-weight: 800; color: #111; margin-bottom: 10px; }
.score-label { color: var(--text-light); font-weight: 500; font-size: 1rem; }
.score-box { font-size: 4rem; font-weight: 800; color: var(--primary); margin: 20px 0 40px; }
.result-actions { display: flex; flex-direction: column; gap: 12px; }
/* Khung tổng thể: Giới hạn độ rộng để không bị quá bự */
.qr-container {
    margin: 25px auto; /* auto giúp căn giữa toàn bộ khối */
    text-align: center;
    border-top: 1px solid #eee;
    padding-top: 20px;
    max-width: 280px;  /* Đặt giới hạn bự nhất của khung là 280px */
}

/* Chữ tiêu đề */
.qr-container p {
    font-size: 14px;
    color: #666;
    margin-bottom: 15px;
    font-weight: bold;
}

/* Khung card trắng: Ôm khít ảnh */
.qr-card-wrapper {
    display: inline-block;
    background: #fff;
    padding: 10px;        /* Giảm padding một chút cho đỡ bự */
    border-radius: 15px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.08);
    line-height: 0;
}

/* Ảnh QR: Chỉnh lại kích thước vừa phải */
.qr-card-wrapper img {
    width: 190px;         /* GIẢM TỪ 230px XUỐNG 180px cho nhỏ gọn */
    height: auto;
    border-radius: 8px;
    display: block;
               }