2018 前端经典面试题

三列布局（左右固定；中间自适应）

一、流体布局

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
	.left {
	    float: left;
	    height: 200px;
	    width: 100px;
	    background-color: red;
	}
	.right {
	    width: 200px;
	    height: 200px;
	    background-color: blue;
	    float: right;
	}
	.main {
	    margin-left: 120px;
	    margin-right: 220px;
	    height: 200px;
	    background-color: green;
	}
    </style>
</head>
<body>
    <div class="container">
        <div class="left"></div>
        <div class="right"></div>
        <div class="main"></div>
    </div>
</body>
</html>

二、绝对定位

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
	.container {
	    position: relative;
	}
	.main {
	    height: 400px;
	    margin: 0 120px;
	    background-color: green;
	}
	.left {
	    position: absolute;
	    width: 100px;
	    height: 300px;
	    left: 0;
	    top: 0;
	    background-color: red;
	}
	.right {
	    position: absolute;
	    width: 100px;
	    height: 300px;
	    background-color: blue;
            right: 0;
	    top: 0;
	}
    </style>
</head>
<body>
    <div class="container">
        <div class="main"></div>
	<div class="left"></div>
	<div class="right"></div>
    </div>
</body>
</html>

三、table布局

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
        .container {
	    display: table;
	    width: 100%;
        }
        .left, .main, .right {
	    display: table-cell;
        }
        .left {
	    width: 200px;
	    height: 300px;
	    background-color: red;
        }
        .main {
	    background-color: blue;
        }
        .right {
	    width: 100px;
	    height: 300px;
	    background-color: green;
        }
    </style>
</head>
<body>
    <div class="container">
	<div class="left"></div>
	<div class="main"></div>
	<div class="right"></div>
    </div>
</body>
</html>

四、flex布局

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
	.container {
            display: flex;
	}
	.main {
            flex-grow: 1;
	    height: 300px;
	    background-color: red;
	}
	.left {
	    order: -1;
	    flex: 0 1 200px;
	    margin-right: 20px;
	    height: 300px;
	    background-color: blue;
	}
	.right {
	    flex: 0 1 100px;
            margin-left: 20px;
	    height: 300px;
	    background-color: green;
	}
    </style>
</head>
<body>
    <div class="container">
	<div class="main"></div>
	<div class="left"></div>
	<div class="right"></div>
    </div>
</body>
</html>

五、圣杯布局

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
	.container {
	    margin-left: 120px;
	    margin-right: 220px;
	}
	.main {
	    float: left;
	    width: 100%;
	    height: 300px;
	    background-color: red;
	}
	.left {
	    float: left;
	    width: 100px;
	    height: 300px;
	    margin-left: -100%;
	    position: relative;
	    left: -120px;
	    background-color: blue;
	}
	.right {
	    float: left;
	    width: 200px;
	    height: 300px;
	    margin-left: -200px;
	    position: relative;
	    right: -220px;
	    background-color: green;
	}
    </style>
</head>
<body>
    <div class="container">
	<div class="main"></div>
	<div class="left"></div>
	<div class="right"></div>
    </div>
</body>
</html>

六、bfc 布局

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
	.left {
	    float: left;
	    height: 200px;
	    width: 100px;
	    margin-right: 20px;
	    background-color: red;
	}
	.right {
	    width: 200px;
	    height: 200px;
	    float: right;
	    margin-left: 20px;
	    background-color: blue;
	}	
	.main {
	    height: 200px;
	    overflow: hidden;
	    background-color: green;
	}
    </style>
</head>
<body>
    <div class="container">
        <div class="left"></div>
        <div class="right"></div>
        <div class="main"></div>
    </div>
</body>
</html>

清除浮动 {父级塌陷}

一、clear清除浮动（添加空div法）

在浮动元素下方添加空div,并给该元素写css样式： {clear:both;height:0;overflow:hidden;}

二、给浮动元素父级设置高度

三、给父级添加overflow:hidden 清浮动方法；

四、 after伪类

.clear:after{content:'';display:block;clear:both;height:0;overflow:hidden;visibility:hidden;}

.clear{zoom:1;}

绝对居住

display：table

负位移

</div>

#parent2{

width: 500px;

height: 300px;

position: relative;

}

#son2{

width: 250px;

height: 150px;

position: absolute;

left: 50%;

top: 50%;

transform: translate(-50%,-50%);

}

display:flex