height: 100% or min-height: 100% for html and body elements?

Question

While designing layouts I set the html, body elements' height to 100% but in some cases, this fails, so what should be used?

html, body {
   height: 100%;
}

or

html, body {
   min-height: 100%;
}

Well, this is not opinion based as each method has its own flaws, so what's the recommended way to go for and why?

Lifework

Answer 1

If you're trying to apply background images to html and body that fill up the entire browser window, neither. Use this instead:

html {
   height: 100%;
}

body {
   min-height: 100%;
}

My reasoning is given here (where I explain holistically how to apply backgrounds in this manner):

Incidentally, the reason why you have to specify height and min-height to html and body respectively is because neither element has any intrinsic height. Both are height: auto by default. It is the viewport that has 100% height, so height: 100% is taken from the viewport, then applied to body as a minimum to allow for scrolling of content.

The first way, using height: 100% on both, prevents body from expanding with its contents once they start to grow beyond the viewport height. Technically this doesn't prevent the content from scrolling, but it does cause body to leave a gap beneath the fold, which is usually undesirable.

The second way, using min-height: 100% on both, doesn't cause body to expand to the full height of html because min-height with a percentage doesn't work on body unless html has an explicit height.

For the sake of completeness, section 10 of CSS2.1 contains all the details, but it's an extremely convoluted read so you can skip it if you're not interested in anything beyond what I've explained here.

Clergy

This is what I liked this most :) height: 100% is taken from the viewport, then applied to body as a minimum to allow for scrolling of content easy peasy solution... thanks // – Lifework

I wonder though, how does the scroll bars magically appear then? The html element has overflow:visible by default, so I assume the scroll bars appear due to browser behavior to allow the whole normal flow of the document to be displayed. – Crumley

@Fabrício Matté: It translates to overflow: auto on the viewport, which is where the scrollbars come from. That's covered in section 11: w3.org/TR/CSS21/visufx.html – Clergy

Wow quick reply, thanks for the direct link to spec as well. =] – Crumley

@Clergy Any idea how to get the child 100% of the body here? this works though – Lifework

@Mr.Alien: Did you find any solution? I despair here :/ – Hegumen

@Julian He had edited his answer after I had commented, you will get the answer in there, use background on html and not on any container element – Lifework

Thanks, @Mr.Alien, but the background should shrink horizontally with the window in a specified range. Sometimes I hate designers... :) Thanks, though – Hegumen

This is the only solution that worked for me, despite there being lots of other answers to similar questions on here. – Knowhow

By the way..maybe do not forget to put the box-sizing:border-box; on all html to elements, to avoid issues with margins and paddings here and there :) – Rightly

box-sizing: border-box doesn't affect margins. Padding, yeah, but that's down to personal preference. – Clergy

Answer 2

You can use viewport height (vh) unit:

body {
    min-height: 100vh;
}

It is relative to screen, not to parent height, so you don't need html height: 100%.

Robles

What extra advantages does this offer though. – Dagan

No extra advantages, just another way to solve the problem. – Robles

beware of how mobile understands this – Matchbook

Just be aware that no all browsers support this units... Do check browser compatibility first: caniuse.com/#feat=viewport-units – Automatize

A warning: viewport-relative units don't take into account scroll bar dimensions. You may end up with an extra few pixels of white space at the bottom of your content, if the page width is overflowing. – Marler