css3 自定义变量和动态计算示例

示例1：
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body {
            /*定义一个变量*/
            --index: 3;
        }

        div {
            /*为了看清，添加一个边框*/
            border: 1px solid blue;
            width: 100px;
            height: 100px;
            background-color: rgb(calc(255/var(--index)),calc(255/var(--index)),calc(255/var(--index)));
        }
    </style>
</head>
<body>
<div></div>
<br/>
<div></div>
</body>
</html>

示例2：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" style="height: 100%;">
<head>
    <title></title>
    <style type="text/css">
        body
        {
            position: relative;
            padding: 0px;
            margin: 0px;
            border-width: 0px;
            width: 100%;
            height: 100%;
            --leftWidth: 300px;
        }
        .left
        {
            position: absolute;
            left: 0px;
            top: 0px;
            bottom: 0px;
            background-color: Red;
            width: var(--leftWidth);
            box-sizing: border-box;
            border:10px solid green;
        }
        .right
        {
            position: absolute;
            top: 0px;
            right: 0px;
            bottom: 0px;
            background-color: Yellow;
            width: calc(100% - var(--leftWidth));
            box-sizing: border-box;
            border:10px solid blue;
        }
    </style>
</head>
<body>
    <div class="left">
    </div>
    <div class="right">
    </div>
</body>
</html>