/* === CÀI ĐẶT CHUNG & BIẾN MÀU === */
body {
    font-family: 'Inter', sans-serif;
    background-color: #f8fafc; /* Màu nền xám nhạt */
}

:root {
    --theme-blue: #002060;
    --theme-red: #C00000;
    --text-light: #6b7280; /* Màu chữ xám nhạt */
}

.text-theme-blue { color: var(--theme-blue); }
.bg-theme-red { background-color: var(--theme-red); }
.text-theme-red { color: var(--theme-red); }
.bg-theme-blue { background-color: var(--theme-blue); }
.border-theme-blue { border-color: var(--theme-blue); }


/* === THIẾT KẾ THẺ CHỌN LỚP (GRADE CARD) === */
.grade-card {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 2rem 1rem;
    background-color: white;
    border-radius: 1rem;
    border: 1px solid #e5e7eb;
    box-shadow: 0 4px 6px -1px rgb(0 0 0 / 0.07), 0 2px 4px -2px rgb(0 0 0 / 0.07);
    text-decoration: none;
    position: relative;
    overflow: hidden;
    transition: transform 0.3s ease, box-shadow 0.3s ease, border-color 0.3s ease;
}
.grade-card:hover {
    transform: translateY(-8px);
    box-shadow: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
    border-color: var(--theme-blue);
}
.grade-card-icon {
    font-size: 3.5rem;
    color: var(--theme-blue);
    margin-bottom: 1rem;
    transition: transform 0.3s ease-in-out, color 0.3s ease;
}
.grade-card:hover .grade-card-icon {
    transform: scale(1.15) rotate(-5deg);
    color: var(--theme-red);
}
.grade-card-title {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--theme-blue);
    transition: color 0.3s ease;
}


/* === [CẬP NHẬT] THIẾT KẾ THẺ THÔNG TIN (Mục tiêu, Nội dung) === */
.info-card {
    background-color: #f3f4f6; /* Nền xám nhạt cho toàn bộ thẻ */
    border-radius: 0.5rem;
    margin-bottom: 1rem;
    overflow: hidden; /* Ẩn phần tràn ra khi bo góc */
}

.info-card-header {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.75rem 1rem;
    cursor: pointer;
    list-style: none;
    font-weight: 600;
}

.info-card-header::-webkit-details-marker {
    display: none;
}

.info-card-header .arrow {
    transition: transform 0.2s ease-in-out;
    color: #6b7280; /* Màu mũi tên xám */
}

.info-card[open] > .info-card-header .arrow {
    transform: rotate(90deg);
}

.info-card-content {
    background-color: #ffffff; /* Nền trắng cho nội dung */
    padding: 1rem;
    color: #374151;
    line-height: 1.6;
    border-top: 1px solid #e5e7eb; /* Đường kẻ phân cách */
}


/* === CÁC PHẦN CSS KHÁC CHO TRANG CHI TIẾT === */

.lesson-link { 
    position: relative;
    transition: all 0.3s ease-in-out;
    cursor: pointer;
    background-color: white;
    border: 1px solid #e5e7eb;
    border-radius: 0.5rem;
    box-shadow: 0 1px 3px 0 rgb(0 0 0 / 0.1), 0 1px 2px -1px rgb(0 0 0 / 0.1);
    padding: 1rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
}
.lesson-link:hover { 
    transform: translateY(-4px); 
    box-shadow: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    border-color: var(--theme-blue);
}

.slide-icon {
    position: absolute;
    top: 0.5rem;
    right: 0.5rem;
    width: 2rem;
    height: 2rem;
    background-color: rgba(0, 32, 96, 0.7);
    color: white;
    border-radius: 9999px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.875rem;
    opacity: 0;
    transform: scale(0.8);
    transition: opacity 0.2s ease, transform 0.2s ease;
    z-index: 10;
}
.lesson-link:hover .slide-icon {
    opacity: 1;
    transform: scale(1);
}
.slide-icon:hover {
    background-color: var(--theme-red);
    transform: scale(1.1) rotate(5deg) !important;
}

.tab-buttons {
    display: flex;
    border-bottom: 2px solid #e5e7eb;
}
.tab-button {
    padding: 0.75rem 1.5rem;
    cursor: pointer;
    border-bottom: 3px solid transparent;
    transition: all 0.3s ease;
    font-weight: 600;
    color: #6b7280;
    margin-bottom: -2px;
}
.tab-button:hover {
    color: var(--theme-blue);
    background-color: #f9fafb;
}
.tab-button.active {
    color: var(--theme-blue);
    border-bottom-color: var(--theme-red);
}
.tab-content {
    display: none;
    padding: 1.5rem;
    background-color: white;
    border: 1px solid #e5e7eb;
    border-top: none;
    border-radius: 0 0 0.5rem 0.5rem;
}
.tab-content.active { display: block; }

.video-container {
    position: relative;
    padding-bottom: 56.25%;
    height: 0;
    overflow: hidden;
    width: 100%;
    border-radius: 0.5rem;
}
.video-container iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

.consolidation-section { margin-bottom: 1.5rem; }
.consolidation-title {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--theme-blue);
    border-bottom: 2px solid #e5e7eb;
    padding-bottom: 0.5rem;
    margin-bottom: 1rem;
}
.consolidation-content ul {
    list-style-type: disc;
    padding-left: 1.5rem;
    color: #374151;
}

.quiz-option {
    display: block;
    width: 100%;
    padding: 12px;
    margin-bottom: 10px;
    border: 2px solid #e5e7eb;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
    text-align: left;
    background-color: white;
}
.quiz-option:hover:not([disabled]) {
    border-color: var(--theme-blue);
    background-color: #f0f9ff;
}
.quiz-option.selected {
    border-color: #3b82f6;
    background-color: #eff6ff;
    font-weight: 600;
}
.quiz-option.correct {
    border-color: #22c55e !important;
    background-color: #dcfce7 !important;
    color: #166534;
}
.quiz-option.incorrect {
    border-color: #ef4444 !important;
    background-color: #fee2e2 !important;
    color: #991b1b;
}
.quiz-option:disabled {
    cursor: not-allowed;
    opacity: 0.8;
}