Saturday, September 21, 2019

CSS 100% height with padding/margin

Answer


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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