CSS 设置 Div 宽度 100% 高度 50px，背景黑色，文字蓝色，链接红色

<style>
div {
  width: 100%;
  height: 50px;
  background-color: black;
  color: blue;
}
a {
  color: red;
}
</style>
<div>
  This is a div with black background and blue text. <a href='#'>This is a link</a> with red color.
</div>