Margin:auto to Push/Pull and item

Margin-hack.css

/* CSS Hack to push/pull a fixed width element left/right without floating. 
   Probably common knowledge but it's new to me. */

/* Margin: auto is often used to center one fixed-width element within another, like so */

#element1 {
  width: 980px;
}

#child1 {
  width: 550px;
  margin: 0 auto;
}

/* turns you can also push the element right or left using just one auto and a 0 for the other side
   e.g. to pull an element to the right without floating & clearing: */

#element1 {
  width: 980px;
}

#child1 {
  width: 550px;
  margin: 0 0 0 auto;
}

/* handy */