Keywords: Web, CSS

HTML Layout:

<div id="father">
  <div id="child">
    Text or image.
  </div>
</div>

CSS3:

#father #child{ background-color: rgba(0,0,0,0.4); }

#father #child{ background-color: rgba(0,0,0,0.4); } would excludes all children elements.

#child{ background-color: rgba(0,0,0,0.4); } would not work, because father's ID must be declared in the front child's ID.

Reference

How do I give text or an image a transparent background using CSS?
https://stackoverflow.com/questions/806000/how-do-i-give-text-or-an-image-a-transparent-background-using-css


人最根本的素质,是让别人放心。