.bd-placeholder-img {
    font-size: 1.125rem;
    text-anchor: middle;
    -webkit-user-select: none;
    -moz-user-select: none;
    user-select: none;
}

@media (min-width: 768px) {
    .bd-placeholder-img-lg {
        font-size: 3.5rem;
    }
}


/* 给导航栏设置背景颜色 */
.navbar {
    display: flex;
    justify-content: center;
}

/* 给导航栏中的链接设置颜色 */
.navbar a {
    color: #f2f2f2;
    padding: 14px 16px;
    text-decoration: none;
    border-radius: 4px;
    border: 1px solid transparent;
}

/* 鼠标移动到链接上时的效果 */
.navbar a:hover {
    background-color: #ddd;
    color: black;
}

/* 选中的标签的样式 */
.navbar a.active {
    background-color: #f3c120;
    color: white;
}