way1:
flex布局：主轴垂直居中 + 侧轴垂直居中
<style>
* {
padding: 0;
margin: 0;
box-sizing: border-box;
}
.bigBox {
width: 300px;
height: 300px;
background-color: plum;
margin: 100px auto 0;
display: flex;
justify-content: center;
align-items: center;
}
.smallBox {
width: 200px;
height: 200px;
background-color: yellowgreen;
}
</style>
<body>
<div class="bigBox">
<div class="smallBox"></div>
</div>
</body>
way2:
父级：相对定位
子级：绝对定位 上下左右0 + margin:auto
<style>
* {
padding: 0;
margin: 0;
box-sizing: border-box;
}
.bigBox {
width: 300px;
height: 300px;
background-color: plum;
margin: 100px auto 0;
position: relative;
}
.smallBox {
width: 200px;
height: 200px;
background-color: yellowgreen;
position: absolute;
margin: auto;
top: 0;
bottom: 0;
right: 0;
left: 0;
}
</style>
way3:
子级：上、左margin = ( 父盒子宽 / 高 - 盒子宽 / 高 ) 的50%(需要计算)
<style>
* {
padding: 0;
margin: 0;
box-sizing: border-box;
}
.bigBox {
width: 300px;
height: 300px;
background-color: plum;
margin: 100px auto 0;
overflow: hidden;
/* padding-top: 50px; */
}
.smallBox {
width: 200px;
height: 200px;
background-color: yellowgreen;
margin-top: 50px;
margin-left: 50px;
}
</style>
way4:
父级：相对定位
子级：绝对定位+距离父盒子上左各50%，再往回移动自己宽高的50%(需要计算)
<style>
* {
padding: 0;
margin: 0;
box-sizing: border-box;
}
.bigBox {
width: 300px;
height: 300px;
background-color: plum;
margin: 100px auto 0;
position: relative;
}
.smallBox {
width: 200px;
height: 200px;
background-color: yellowgreen;
position: absolute;
top: 50%;
left: 50%;
margin-top: -100px;
margin-left: -100px;
}
</style>
way5:
父级：相对定位
子级：绝对定位+距离父盒子上左各50%，再x、y轴各移动自己的50%
(不需要计算，直接使用位移)
<style>
* {
padding: 0;
margin: 0;
box-sizing: border-box;
}
.bigBox {
width: 300px;
height: 300px;
background-color: plum;
margin: 100px auto 0;
position: relative;
}
.smallBox {
width: 200px;
height: 200px;
background-color: yellowgreen;
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
}
</style>
way6:
父级：display: table-cell + 基线对齐 + 文字居中对齐
子级：转行内块
注意：display:table-cell的属性很类似于td标签，并且对margin值是没有任何意义的
<style>
* {
padding: 0;
margin: 0;
box-sizing: border-box;
}
.bigBox {
width: 300px;
height: 300px;
background-color: plum;
/* margin: 100px auto 0; */
display: table-cell;
vertical-align: middle;
text-align: center;
}
.smallBox {
width: 200px;
height: 200px;
background-color: yellowgreen;
display: inline-block;
}
</style>