/* 顶部横幅区域 */
.header-row {
    width: 100%;
    display: flex;
    flex-direction: row;
    align-items: center;
    justify-content: flex-start;
    margin-bottom: 24px;
}

/* 让.course-title独占一行 */
.course-title {
    width: 100%;
    display: block;
    margin-bottom: 24px;
    background: #fff;
    border-radius: 10px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.07);
    padding: 24px 32px 18px 32px;
    box-sizing: border-box;
}

/* 让main-layout只负责下方三栏 */
.main-layout {
    max-width: 1200px;
    margin: 0 auto;
    width: 100%;
    box-sizing: border-box;
    display: flex;
    flex-direction: column;
    gap: 0;
    margin-top: 0;
}

/* 下方三栏区域 */
.main-left, .main-center, .main-right {
    background: #f8f9fa;
    border-radius: 10px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.07);
    padding: 5px;
    min-width: 0;
    box-sizing: border-box;
}

.main-row {
    width: 100%;
    box-sizing: border-box;
    display: flex;
    flex-direction: row;
    gap: 32px;
}
.main-left { width: 220px; min-width: 180px; }
.main-center { flex: 1 1 0; min-width: 500px; }
.main-right { width: 200px; min-width: 140px; }
/*参考斯坦福大学*/
.card {
    --bs-card-spacer-y: 1rem;
    --bs-card-spacer-x: 1rem;
    --bs-card-title-spacer-y: 0.5rem;
    --bs-card-title-color: ;
    --bs-card-subtitle-color: ;
    --bs-card-border-width: var(--bs-border-width);
    --bs-card-border-color: var(--bs-border-color-translucent);
    --bs-card-border-radius: var(--bs-border-radius);
    --bs-card-box-shadow: ;
    --bs-card-inner-border-radius: calc(var(--bs-border-radius) - var(--bs-border-width));
    --bs-card-cap-padding-y: 0.5rem;
    --bs-card-cap-padding-x: 1rem;
    --bs-card-cap-bg: rgba(var(--bs-body-color-rgb),0.03);
    --bs-card-cap-color: ;
    --bs-card-height: ;
    --bs-card-color: ;
    --bs-card-bg: var(--bs-body-bg);
    --bs-card-img-overlay-padding: 1rem;
    --bs-card-group-margin: 0.75rem;
    word-wrap: break-word;
    background-clip: initial;
    background-color: var(--bs-card-bg);
    border: var(--bs-card-border-width) solid var(--bs-card-border-color);
    border-radius: var(--bs-card-border-radius);
    color: #212529;
    color: var(--bs-body-color);
    display: flex;
    flex-direction: column;
    height: var(--bs-card-height);
    min-width: 0;
    position: relative
}

.card>hr {
    margin-left: 0;
    margin-right: 0
}

.card>.list-group {
    border-bottom: inherit;
    border-top: inherit
}

.card>.list-group:first-child {
    border-top-left-radius: var(--bs-card-inner-border-radius);
    border-top-right-radius: var(--bs-card-inner-border-radius);
    border-top-width: 0
}

.card>.list-group:last-child {
    border-bottom-left-radius: var(--bs-card-inner-border-radius);
    border-bottom-right-radius: var(--bs-card-inner-border-radius);
    border-bottom-width: 0
}

.card>.card-header+.list-group,.card>.list-group+.card-footer {
    border-top: 0
}

.card-body {
    color: var(--bs-card-color);
    flex: 1 1 auto;
    padding: var(--bs-card-spacer-y) var(--bs-card-spacer-x)
}

.card-title {
    color: var(--bs-card-title-color);
    margin-bottom: var(--bs-card-title-spacer-y)
}

.card-subtitle {
    color: var(--bs-card-subtitle-color);
    margin-top: calc(var(--bs-card-title-spacer-y)*-.5)
}

.card-subtitle,.card-text:last-child {
    margin-bottom: 0
}

.card-link+.card-link {
    margin-left: var(--bs-card-spacer-x)
}

.card-header {
    background-color: var(--bs-card-cap-bg);
    border-bottom: var(--bs-card-border-width) solid var(--bs-card-border-color);
    color: var(--bs-card-cap-color);
    margin-bottom: 0;
    padding: var(--bs-card-cap-padding-y) var(--bs-card-cap-padding-x)
}

.card-header:first-child {
    border-radius: var(--bs-card-inner-border-radius) var(--bs-card-inner-border-radius) 0 0
}

.card-footer {
    background-color: var(--bs-card-cap-bg);
    border-top: var(--bs-card-border-width) solid var(--bs-card-border-color);
    color: var(--bs-card-cap-color);
    padding: var(--bs-card-cap-padding-y) var(--bs-card-cap-padding-x)
}

.card-footer:last-child {
    border-radius: 0 0 var(--bs-card-inner-border-radius) var(--bs-card-inner-border-radius)
}

.card-header-tabs {
    border-bottom: 0;
    margin-bottom: calc(var(--bs-card-cap-padding-y)*-1);
    margin-left: calc(var(--bs-card-cap-padding-x)*-.5);
    margin-right: calc(var(--bs-card-cap-padding-x)*-.5)
}

.card-header-tabs .nav-link.active {
    background-color: var(--bs-card-bg);
    border-bottom-color: var(--bs-card-bg)
}

.card-header-pills {
    margin-left: calc(var(--bs-card-cap-padding-x)*-.5);
    margin-right: calc(var(--bs-card-cap-padding-x)*-.5)
}

.card-img-overlay {
    border-radius: var(--bs-card-inner-border-radius);
    bottom: 0;
    left: 0;
    padding: var(--bs-card-img-overlay-padding);
    position: absolute;
    right: 0;
    top: 0
}

.card-img,.card-img-bottom,.card-img-top {
    width: 100%
}

.card-img,.card-img-top {
    border-top-left-radius: var(--bs-card-inner-border-radius);
    border-top-right-radius: var(--bs-card-inner-border-radius)
}

.card-img,.card-img-bottom {
    border-bottom-left-radius: var(--bs-card-inner-border-radius);
    border-bottom-right-radius: var(--bs-card-inner-border-radius)
}

.card-group>.card {
    margin-bottom: var(--bs-card-group-margin)
}

@media (min-width: 576px) {
    .card-group {
        display:flex;
        flex-flow: row wrap
    }

    .card-group>.card {
        flex: 1 0;
        margin-bottom: 0
    }

    .card-group>.card+.card {
        border-left: 0;
        margin-left: 0
    }

    .card-group>.card:not(:last-child) {
        border-bottom-right-radius: 0;
        border-top-right-radius: 0
    }

    .card-group>.card:not(:last-child) .card-header,.card-group>.card:not(:last-child) .card-img-top {
        border-top-right-radius: 0
    }

    .card-group>.card:not(:last-child) .card-footer,.card-group>.card:not(:last-child) .card-img-bottom {
        border-bottom-right-radius: 0
    }

    .card-group>.card:not(:first-child) {
        border-bottom-left-radius: 0;
        border-top-left-radius: 0
    }

    .card-group>.card:not(:first-child) .card-header,.card-group>.card:not(:first-child) .card-img-top {
        border-top-left-radius: 0
    }

    .card-group>.card:not(:first-child) .card-footer,.card-group>.card:not(:first-child) .card-img-bottom {
        border-bottom-left-radius: 0
    }
}
.announcement {
    background-color: #f5fafd;
    border-style: none;
    padding: 18px;
    border-radius: 8px;
    margin-bottom: 10px;
    
}

.card.announcement ul {
    list-style: none;
    padding-left: 0;
    margin: 0.5em 0;
}

.card.announcement li {
    text-indent: -1.5em;
    padding-left: 1.5em;
    margin-bottom: 0.25em;
}
.card.announcement li a{
    color: #337ab7;
    padding-left: 1.5em;
   
}

/* card有关复制的 */

/* 让main-left/main-center/main-right在main-row内排列 */
.main-layout > .main-left,
.main-layout > .main-center,
.main-layout > .main-right {
    margin-top: 0;
}

/* 兼容原有样式 */
.logo { width: 90px; margin-bottom: 0; }
.course-title h1 { font-size: 2.3rem; margin-bottom: 0.3rem; }

/* 让main-content有背景色和内边距 */
.main-content {
    background: #fff;
    border-radius: 12px;
    padding: 5px 5px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.04);
   
}

/* 右侧资源区分组样式 */
.section { margin-top: 24px; }
.section h3 { font-size: 1.1rem; margin-bottom: 8px; color: #888; font-weight: 600; letter-spacing: 1px; }
.section ul { padding-left: 1px; }
.instructor { display: flex; align-items: center; margin-bottom: 12px; }
.instructor img { width: 60px; height: 60px; border-radius: 8px; margin-right: 12px; }
.main-content h2 { font-size: 1.5rem; margin-bottom: 1rem; }
.main-right .section h3,
.main-right .section ul {
    text-align: left !important;
}
.main-right .section li {
    text-align: left;
    align-items: flex-start;
    justify-content: flex-start;
}
.main-right .section ul li a {
    display: flex;
    align-items: center;
    color: #1976d2;
    text-decoration: none;
    font-size: 1.15em;
}
.main-right .section ul li a svg {
    margin-right: 6px;
    flex-shrink: 0;
}