第四课--背景background:#ffffff url('img_tree.<link rel="styleshee

CSS 属性定义背景效果:
background-color
background-image
background-repeat
background-attachment
background-position
水平或垂直平铺：
background-repeat:repeat-x;
背景图像- 设置定位与不平铺
background-repeat:no-repeat;
简写属性
background:#ffffff url('img_tree.png') no-repeat right top;
当使用简写属性时，属性值的顺序为：:
background-color
background-image
background-repeat
background-attachment
background-position

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>背景</title>
    <link rel="stylesheet" href="demo.css">
</head>
<body>
<h1>Hello World!</h1>
<p>该文本不容易被阅读。</p>
</body>
</html>

body {
    /*背景颜色*/
    /*background-color: #FFA500;*/
    /*背景图像*/
    /*background-image:url('demo.png');*/
    /*水平或垂直平铺*/
    /*background-repeat:repeat-x;!*repeat-y*!*/
    /*设置定位与不平铺*/
    /*background-repeat:no-repeat;*/
    /*简写属性*/
    /*background: #FFA500 url('demo.png') no-repeat right top;*/

    /*文本颜色*/
    color: red;
}