Question

Is it possible somehow to calculate size of an element as a basic mathematical expression?
e.g.:

.wideColumn{max-width:100%-20em;} /*not working*/

Answer 1

This can be accomplished using LESS or jQuery. But unfortunately it cannot be done with pure CSS.

There are, however, workarounds to this issue using pure CSS. For example:

.wideColumn {
    max-width: 100%;
    margin-right: 10em;
    margin-left: 10em;
}

Of course, this example may not work with your code. But there are numerous other workarounds.