position左右布局.png

代码：

<p>position左右布局</p>
    <div class="container1">
        <div class="box1"></div>
        <div class="box2"></div>
    </div>

.container1, .container2 {
    border: 2px solid black;
    max-width: 450px;
    height: 250px;
    margin: 0 auto;
    box-sizing: border-box;
    position: relative;
}

.container1 .box1 {
    width: 200px;
    height: 200px;
    border: 2px solid red;
    position: absolute;
    top: 0;
    left: 0;
}

.container1 .box2 {
    width: 200px;
    height: 200px;
    border: 2px solid blue;
    position: absolute;
    top: 0;
    right: 0;
}

float左右布局.png

<p>float左右布局</p>
    <div class="container2 clearfix">
        <div class="box3"></div>
        <div class="box4"></div>
    </div>

.clearfix::after {
    content: '';
    display: block;
    clear: both;
}
.container2 .box3 {
    width: 200px;
    height: 200px;
    border: 2px solid red;
    float: left;
}

.container2 .box4 {
    width: 200px;
    height: 200px;
    border: 2px solid blue;
    float: right;
}

postion左中右布局.png

<p>position左中右布局</p>
    <div class="container3">
        <div class="box5"></div>
        <div class="box6"></div>
        <div class="box7"></div>
    </div>

.container3 {
    border: 2px solid black;
    max-width: 700px;
    height: 300px;
    margin: 0 auto;
    position: relative;
}

.container3 .box5 {
    width: 200px;
    height: 200px;
    border: 2px solid red;
    position: absolute;
    top: 0;
    left: 0;
}

.container3 .box6 {
    width: 200px;
    height: 200px;
    border: 2px solid yellow;
    position: absolute;
    top: 0;
    left: 250px;

}

.container3 .box7 {
    width: 200px;
    height: 200px;
    border: 2px solid green;
    position: absolute;
    top: 0;
    right: 0;
}

flex水平垂直居中.png

<p>flex水平垂直居中</p>
    <div class="container4">
        <div class="box8"></div>
    </div>

.container4 {
    border: 2px solid black;
    max-width: 450px;
    height: 250px;
    margin: 0 auto;
    display: flex;
    align-items: center;
}
.container4 .box8 {
    width: 200px;
    height: 200px;
    border: 2px solid red;
    margin: 0 auto;
}

水平居中
行内元素liline

p {
    text-align: center;
}

块级元素block

div {
     margin: 0 auto;
}

多块级元素block
对其父级元素设置text-align: center;然后子级元素display: inline-block；
或者使用flex布局
垂直居中
行内元素inline
单行：设置上下相等的paddding，或者设置line-height
多行：设置上下相等的paddding，或者vertical-align:middle;；或者使用flex布局
块级元素block
flex布局