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

Setting the body margins to 0, the width of the outer container to 100%, and using an inner container with 50px left/right margins seems to work.

  

    

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