水平居中
1.文本居中对齐
内联元素(给容器添加样式)
限制条件:仅用于内联元素 display:inline 和 display: inline-block;
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>Document</title><style>.box {margin: 30px 30px 0px 300px;border: 1px solid gray;text-align: center;}.item {display: inline-block;width: 400px;background: yellow;}</style></head><body><div class="box"><span>水平居中 -- display: inline</span></div><div class="box"><div class="item">水平居中 -- display: inline-block</div></div></body>
</html>
自动外边距(块级元素)
限制条件:仅用于块级元素 display:block;
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>Document</title><style>.box {margin: 30px;border: 1px solid gray;}.item {margin: auto;width: 300px;background: yellow;}</style></head><body><div class="box"><div class="item">水平居中 -- 块级元素 display:block</div></div></body>
</html>
flex布局
给容器添加样式 :display: flex; justify-content: center; ()
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>Document</title><style>.box {margin: 30px 30px 0px 300px;border: 1px solid gray;display: flex;justify-content: center;}.item {width: 400px;background: yellow;}</style></head><body><div class="box"><span>水平居中 -- flex布局 display: inline</span></div><div class="box"><div class="item">水平居中 -- flex布局 display: block</div></div></body>
</html>
子绝父相 + transform (CSS3)
限制条件:浏览器需支持CSS3,比较老的浏览器不适用
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
left: 50%;
transform: translate(-50%, 0);
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>Document</title><style>.box {margin: 30px 30px 0px 300px;border: 1px solid gray;height: 50px;position: relative;}.item {background-color: yellow;position: absolute;left: 50%;transform: translate(-50%, 0);}</style></head><body><div class="box"><span class="item">水平居中 -- 子绝父相 + transform</span></div></body>
</html>
子绝父相 + 自动外边距 (指定宽度)
限制条件:内部元素需限定宽度
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute; left: 0; right: 0; margin: auto;
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>Document</title><style>.box {margin: 30px 30px 0px 300px;border: 1px solid gray;height: 50px;position: relative;}.item {background-color: yellow;position: absolute;left: 0;right: 0;margin: auto;width: 300px;}</style></head><body><div class="box"><span class="item">水平居中 -- 子绝父相 + 自动外边距</span></div></body>
</html>
子绝父相 + 负外边距 (知道宽度 + 宽度计算)不退推荐
限制条件:需知道内部元素的宽度(无法预知宽度的内联元素和未知宽度的块级元素都不适用)
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
left:50%;
margin-left:-内部元素宽度的一半
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>Document</title><style>.box {margin: 30px;border: 1px solid gray;height: 100px;position: relative;}.item {width: 400px;background: yellow;position: absolute;left: 50%;margin-left: -200px;}</style></head><body><div class="box"><div class="item">水平居中 -- 绝对定位元素 position:absolute</div></div></body>
</html>