* {
    box-sizing: border-box;
}
 
/* body 样式 */
body {
    font-family: Arial;
    margin: 0;
}
 
/* 标题 */
.header {
    padding: 20px;
    text-align: center;
    background: linear-gradient(#454545,black);
    color: white;
}
 
/* 标题字体 */
.header h1 {
    font-size: 40px;
    text-shadow: 0 0 10px red,0 0 20px red,0 0 40px red,0 0 40px red;
}
/* 定义动画关键帧 */
@keyframes fade-in {
    0% {
            opacity: 0;
    }
    100% {
            opacity: 1;
    }
}

/* 应用动画效果 */
.delay-text {
    animation: fade-in 2s ease-in-out;
}
 
/* 导航 */
.navbar {
    overflow: hidden;
    background-color: black;
}
 
/* 导航栏样式 */
.navbar a {
    float: left;
    display: #333;
    color: white;
    text-align: center;
    padding: 14px 20px;
    text-decoration: none;
}

.dropdown {
    display: inline-block;
    float: left;
}

.dropdown-content {
    display: none;
    position: absolute;
    background-color: black;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
}

.dropdown-content a {
    color: white;
    padding: 12px 16px;
    text-decoration: none;
    display: white;
}

.dropdown-content a:hover {background-color: #333}

.dropdown:hover .dropdown-content {
    display: block;
}

/* 右侧链接*/
.navbar a.right {
    float: right;
}
 
/* 鼠标移动到链接的颜色 */
.navbar a:hover {
    background-color: #ddd;
    color: black;
}
 
/* 列容器 */
.row {  
    display: -ms-flexbox; /* IE10 */
    display: flex;
    -ms-flex-wrap: wrap; /* IE10 */
    flex-wrap: wrap;
}
 
/* 创建两个列 */
/* 边栏 */
.side {
    -ms-flex: 20%; /* IE10 */
    flex: 20%;
    background: linear-gradient(black, #FF2222);
    padding: 20px;
    color: white;
}
 
/* 主要的内容区域 */
.main {   
    -ms-flex: 70%; /* IE10 */
    flex: 70%;
    background-color: white;
    padding: 20px;
}
/* 新闻 */
#news {
    color:red;
    animation: fade-in 2s ease-in-out;
}
 
/* 测试图片 */
.fakeimg {
    width: 100%;
    padding: 20px;
}
 
/* 底部 */
.footer {
    padding: 20px;
    text-align: left;
    background: linear-gradient(black, #454545);
    color: white;
}
/* 响应式布局 - 在屏幕设备宽度尺寸小于 700px 时, 让两栏上下堆叠显示 */
@media screen and (max-width: 700px) {
    .row {   
        flex-direction: column;
    }
}
 
/* 响应式布局 - 在屏幕设备宽度尺寸小于 400px 时, 让导航栏目上下堆叠显示 */
@media screen and (max-width: 400px) {
    .navbar a {
        float: none;
        width: 100%;
    }
}
/* B站视频 */
.aspect-ratio {
    position: relative;
    width: 100%;
    height: 0;
    padding-bottom: 75%;
}

.aspect-ratio iframe {
    position: absolute;
    width: 60%;
    height: 50%;
    left: 0;
    top: 0;
}