cssstyle.css
#div1{color:blue}
#div2{color:gold}
#div3{color:red}
css.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<!--
<link type="text/css" href="cssstyle.css"rel="stylesheet">
-->
<link type="text/css" href="cssstyle.css" rel="stylesheet">
</head>
<body>
<!--<p style="color:red;background:blue">这里可以加颜色</p>-->
<div id="div1">这里给div添色1</div>
<div id="div2">这里给div添色2</div>
<div id="div3">这里给div添色3</div>
</body>
</html>