How can I do width = 100% - 100px in CSS?

Question

In CSS, how can I do something like this:

width: 100% - 100px;

I guess this is fairly simple but it is a bit hard to find examples showing

Answer 1

Modern browsers now support the:

width: calc(100% - 100px);

To see the list of supported browser versions checkout: Can I use calc() as CSS unit value?

There is a jQuery fallback: css width: calc(100% -100px); alternative using jquery