Fixed sidebar columns problem

I need to have fixed sidebars (not sidebars from WordPress point of view – just columns with fixed width from left and right).
Ok, let’s start from 3 columns percentages:
10% 80% 10%
Seems good except 1st and 3rd resizing.
Now it looks like:

--|----------------|---

Ok, apply the styles to 1st and 3rd columns:

.left-sidebar {
  margin-left: 0px;
  width: 120px;
}
.right-sidebar {
  margin-right: 0px;
  width: 120px;
}

Layout before:

--|----------------|---

After styling:

-|----------------|-

What’s happened – 1st and 3rd columns become narrower, but 2nd has width calculated before and overall columns don’t occupy all screen width.
So, how to tell to 2nd column? – “please occupy all the rest between 1st and 3rd columns”.
Same as for HTML tables – “width: *’ – fill all.