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CSS 定位 relative && absolute 问题？

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CSS 定位 relative && absolute 问题？

谁能解释一下，为什么div使用 relative是设置right,bottom 后，看不到div 呀，哪里多出来的 top , left 属性负值呀？

（已测试了所有最新的浏览器，自动添加的top , left 属性负值）

demo:

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<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>CSS 定位：relative &&  absolute</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html,body{
            width: 100%;
            height: 100%;
            background: rgba(0,0,0,0.3);
            color: red;
            box-sizing: border-box;
            overflow: hidden;
        }   
       .relative{           
            background-color: #f0f;
            width: 100px;
            height: 100px;
            position: relative;           
            right: 100px;
            bottom: 100px;
            /*
                position: relative; 浏览器，自动补全 :
                left == -right;
                top == -bottom;
            */
        }      
    </style>
</head>
<body>
    <div class="box">
        <div class="relative">
            <!--comments-->
        </div>
    </div>
</body>
</html>

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2. chrome 中修改后，

3. 同样，设置 left,top 后， 多出来 right/bottom 的负值属性？

 

 

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demo:

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<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>CSS 定位：relative &&  absolute</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html,body{
            width: 100%;
            height: 100%;
            background: rgba(0,0,0,0.3);
            color: red;
            box-sizing: border-box;
            overflow: hidden;
        }
        .box{
            width: 1000px;
            height: 600px;
            border: 1px solid red;
            /*overflow: hidden;*/
        }   
        .box .relative{           
            background-color: #f0f;
            width: 100px;
            height: 100px;
            position: relative;           
            right: 50px;
            bottom: 50px;
            /*
                position: relative; 浏览器，自动补全 :
                left == -right;
                top == -bottom;
            */
        }
        .box .relative-new{
            background-color: #0f0;
            width: 100px;
            height: 100px;
            position: relative;           
            right: 0;
            bottom: 0;
        }      
    </style>
</head>
<body>
    <div class="box">
        <div class="relative">
            <h3>relative</h3>
        </div>
        <div class="relative-new">
            <h3>relative-new</h3>
        </div>
    </div>
</body>
</html>

 

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demo:

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<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>CSS 定位：relative &&  absolute</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html,body{
            width: 100%;
            height: 100%;
            background: rgba(0,0,0,0.3);
            color: red;
            box-sizing: border-box;
            overflow: hidden;
        }
        .box{
            width: 1000px;
            height: 600px;
            border: 1px solid red;
            /*overflow: hidden;*/
        }   
        .box .relative{           
            background-color: #0f0;
            width: 100px;
            height: 100px;
            position: relative;           
            right: 100px;
            bottom: 100px;
            /*
            */
        }
        .box .relative-new{
            background-color: #0f0;
            width: 100px;
            height: 100px;
            position: relative;           
            left: 100px;
            top: 100px;
        }
        .box .absolute{           
            background-color: #0f0;
            width: 100px;
            height: 100px;
            position: absolute;           
            right: 100px;
            bottom: 100px;
            /*
                position:absolute;
                right: 200px;
                bottom: 200px;
                这样才好使！
                //position:absolute; float脱离文档流
            */
        }       
    </style>
</head>
<body>
    <div class="box">
        <div class="relative">
            <h3>relative</h3>
        </div>
        <div class="relative-new">
            <h3>relative-new</h3>
        </div>
        <div class="absolute">
            <h3>absolute</h3>
        </div>
    </div>
</body>
</html>

 

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