CSS: 100% width or height while keeping aspect ratio?

Question

Currently, with STYLE, I can use width: 100% and auto on the height (or vice versa), but I still can\'t constrain the image into a specific positio

Answer 1

Some years later, looking for the same requirement, I found a CSS option using background-size.

It is supposed to work in modern browsers (IE9+).

And the style:

#container
{
  width:  100px; /*or 70%, or what you want*/
  height: 200px; /*or 70%, or what you want*/
  background-size: cover;
  background-position: center;
  background-repeat: no-repeat;
}

The reference: http://www.w3schools.com/cssref/css3_pr_background-size.asp

And the demo: http://www.w3schools.com/cssref/playit.asp?filename=playcss_background-size