外部css文件怎么写 css文件怎么写

@charset "utf-8";

选择器 {
    属性名1: 属性值1,
    属性名2: 属性值2,
    ...
}

<style>
@charset "utf-8";
body{
    margin: 0;
    background: #f9f9f9;
}
.shadow{
    background: #fff;
    box-shadow: 0 0 4px rgba(0, 0, 0, .2);
}
#nav{
    box-sizing: border-box;
    padding: 8px;
    height: 46px;
}
#app{
    margin: 8px;
    min-height: 300px;
}
#footer{
    box-sizing: border-box;
    padding: 8px;
    min-height: 46px
}
</style>
<div class="shadow" id="nav">nav</div>
<div class="shadow" id="app">app</div>
<div class="shadow" id="footer">footer</div>