calc() lets you do a simple calculation, for
CSS property values.
It can be used anywhere that requires a length or number.
width: calc(100% - 80px);
you can use any of the following operators:
- Add. (must have space before and after)
- Subtract. (must have space before and after)
- Times. One of the argument must be a number.
- Divide. The right-hand side must be a number.
Parentheses can be used for grouping.