30秒学会 CSS 片段 – Transform centering

Vertically and horizontally centers a child element within its parent element using position: absolute and transform: translate() (as an alternative to flexbox or display: table).
Similar to flexbox, this method does not require you to know the height or width of your parent or child so it is ideal for responsive applications.

• position: absolute on the child element allows it to be positioned based on its containing block.
• left: 50% and top: 50% offsets the child 50% from the left and top edge of its containing block.
• transform: translate(-50%, -50%) allows the height and width of the child element to be negated so that it is vertically and horizontally centered.
• Note that the fixed height and width on parent element is for the demo only.

预览

HTML

<div class="parent">
  <div class="child">Centered content</div>
</div>

CSS

.parent {
  border: 1px solid #333;
  height: 250px;
  position: relative;
  width: 250px;
}

.child {
  left: 50%;
  position: absolute;
  top: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
}

翻译自：https://www.30secondsofcode.org/css/s/transform-centering