css calc() attribute value

by thmain

HTML

<div class="outer">
  <div class="inner"></div>
</div>

CSS

.outer {
  width: 500px;
  height: 100px;
  background: #dadada;
}

.inner {
  width: calc(100% - 40px);
  height: 50px;
  margin: auto;
  border: 1px solid blue;
}