How to make a div fill a remaining horizontal space?

Question

I have 2 divs: one in the left side and one in the right side of my page. The one in the left side has fixed width and I want the one of the right side to f

Answer 1

If you don't need compatibility with older versions of certain browsers (IE 10 8 or less for example) you can use the calc() CSS function:

#left {
   float:left;
   width:180px;
   background-color:#ff0000;
}

#right {
   float: left;
   width: calc(100% - 180px);
   background-color:#00FF00;
}