[Web][CSS]How to give text or an image a transparent background?

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); }

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

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