[css] How to make padding:auto work in CSS?

The simplest supported solution is to either use margin

.element {
  display: block;
  margin: 0px auto;
}

Or use a second container around the element that has this margin applied. This will somewhat have the effect of padding: 0px auto if it did exist.

CSS

.element_wrapper {
  display: block;
  margin: 0px auto;
}
.element {
  background: blue;
}

HTML

<div class="element_wrapper">
  <div class="element">
    Hello world
  </div>
</div>