.course-detail-header {
    background: linear-gradient(rgba(26, 54, 93, 0.9), rgba(26, 54, 93, 0.9)), url('https://images.unsplash.com/photo-1524178232363-1fb2b075b655?ixlib=rb-1.2.1&auto=format&fit=crop&w=1350&q=80');
    background-size: cover;
    background-position: center;
    padding: 80px 0;
    color: white;
    margin-bottom: 40px;
}

.breadcrumb-item + .breadcrumb-item::before {
    color: rgba(255, 255, 255, 0.6);
}

.course-main-img {
    border-radius: 12px;
    width: 100%;
    height: 450px;
    object-fit: cover;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
}

/* 右欄不隨左欄拉伸，讓 sticky 在 sidebar 內容結束後自動解除 */
main .row > .col-lg-4 {
    align-self: flex-start;
}

.course-sidebar-card {
    background: white;
    border-radius: 12px;
    padding: 25px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
    position: sticky;
    top: 100px;
    border-top: 5px solid var(--secondary-accent);
}

.price-tag {
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--secondary-accent);
    margin-bottom: 20px;
}

.price-tag small {
    font-size: 1rem;
    color: #718096;
    font-weight: 400;
}

.action-btns .btn {
    padding: 12px;
    font-weight: 700;
    border-radius: 8px;
    margin-bottom: 12px;
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    transition: all 0.3s ease;
}

.btn-register {
    background-color: var(--secondary-accent);
    border-color: var(--secondary-accent);
    color: white;
}

.btn-register:hover {
    background-color: #e65c00;
    border-color: #e65c00;
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(255, 102, 0, 0.3);
}

.btn-favorite {
    background-color: #f7fafc;
    border-color: #e2e8f0;
    color: #4a5568;
}

.btn-favorite:hover {
    background-color: #edf2f7;
    border-color: #cbd5e0;
    color: var(--primary-color);
}

.btn-favorite.active {
    color: #e53e3e;
    border-color: #fed7d7;
    background-color: #fff5f5;
}

.course-meta-info {
    list-style: none;
    padding: 0;
    margin: 20px 0;
}

.course-meta-info li {
    display: flex;
    margin-bottom: 15px;
    font-size: 0.95rem;
    color: #4a5568;
}

.course-meta-info li i {
    width: 25px;
    color: var(--primary-color);
    margin-right: 10px;
    margin-top: 4px;
}

.course-meta-info li strong {
    color: #2d3748;
    min-width: 80px;
}

.nav-tabs-custom {
    border-bottom: 2px solid #e2e8f0;
    margin-bottom: 30px;
}

.nav-tabs-custom .nav-link {
    border: none;
    border-bottom: 3px solid transparent;
    color: #718096;
    font-weight: 700;
    padding: 15px 25px;
    transition: all 0.2s;
}

.nav-tabs-custom .nav-link:hover {
    color: var(--primary-color);
}

.nav-tabs-custom .nav-link.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
    background: transparent;
}

.instructor-card {
    background: #f8fafc;
    border-radius: 12px;
    padding: 30px;
    display: flex;
    gap: 25px;
    align-items: flex-start;
    margin-top: 20px;
}

.instructor-img {
    width: 120px;
    height: 120px;
    border-radius: 50%;
    object-fit: cover;
    border: 4px solid white;
    box-shadow: 0 4px 10px rgba(0,0,0,0.1);
}

.difficulty-badge {
    font-size: 0.8rem;
    padding: 5px 12px;
    border-radius: 50px;
    font-weight: 700;
    letter-spacing: 0.5px;
}

.difficulty-easy { background: #c6f6d5; color: #22543d; }
.difficulty-medium { background: #feebc8; color: #744210; }
.difficulty-hard { background: #fed7d7; color: #742a2a; }

.content-section p {
    line-height: 1.8;
    color: #2d3748;
    font-size: 1.05rem;
}

.social-share {
    display: flex;
    gap: 10px;
    margin-top: 20px;
}

.share-btn {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    text-decoration: none;
    transition: transform 0.2s;
}

.share-btn:hover {
    transform: scale(1.1);
    color: white;
}

.share-fb { background: #3b5998; }
.share-line { background: #00c300; }
.share-twitter { background: #1da1f2; }

@media (max-width: 991.98px) {
    .course-main-img {
        height: 300px;
    }
    .course-sidebar-card {
        position: static;
        margin-top: 30px;
    }
}