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Constant width to height ratio  layout

Given an element of variable width, it will ensure its height remains proportionate in a responsive fashion (i.e., its width to height ratio remains constant).

HTML
<div class="constant-width-to-height-ratio"></div>
CSS
.constant-width-to-height-ratio {
  background: #333;
  width: 50%;
}
.constant-width-to-height-ratio::before {
  content: '';
  padding-top: 100%;
  float: left;
}
.constant-width-to-height-ratio::after {
  content: '';
  display: block;
  clear: both;
}
Demo
Explanation
  • padding-top on the ::before pseudo-element causes the height of the element to equal a percentage of its width. 100% therefore means the element's height will always be 100% of the width, creating a responsive square.
  • This method also allows content to be placed inside the element normally.
Browser support

100.0%