CSS 100% height with padding/margin

Saturday, September 21, 2019

CSS 100% height with padding/margin

Answer

With HTML/CSS, how can I make an element that has a width and/or height that is 100% of it's parent element and still has proper padding or margins?

By "proper" I mean that if my parent element is 200px tall and I specify height = 100% with padding = 5px I would expect that I should get a 190px high element with border = 5px on all sides, nicely centered in the parent element.

Now, I know that that's not how the standard box model specifies it should work (although I'd like to know why, exactly...), so the obvious answer doesn't work:

#myDiv {
    width: 100%
    height: 100%;

    padding: 5px;
}

But it would seem to me that there must be SOME way of reliably producing this effect for a parent of arbitrary size. Does anyone know of a way of accomplishing this (seemingly simple) task?

Oh, and for the record I'm not terribly interested in IE compatibility so that should (hopefully) make things a bit easier.

EDIT: Since an example was asked for, here's the simplest one I can think of:

The challenge is then to get the black box to show up with a 25 pixel padding on all edges without the page growing big enough to require scrollbars.

Answer

I learned how to do these sort of things reading "PRO HTML and CSS Design Patterns". The display:block is the default display value for the div, but I like to make it explicit. The container has to be the right type; position attribute is fixed, relative, or absolute.

.stretchedToMargin {
  display: block;
  position:absolute;
  height:auto;
  bottom:0;
  top:0;
  left:0;

  right:0;
  margin-top:20px;
  margin-bottom:20px;
  margin-right:80px;
  margin-left:80px;
  background-color: green;
}


  Hello, world

Fiddle by Nooshu's comment

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Saturday, September 21, 2019

CSS 100% height with padding/margin

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