CSS: Height of textarea as a percentage of the viewport height


I'd like to say that the height of a text area is equal to, say, 50% of the height of the viewport. How can I do that? A simple height: 50% doesn't do the trick.

Best Answer

A simple height: 50% doesn't do the trick.

No, because its parent doesn't have an explicit height. So 50% of what? Parent says ‘auto’, which means base it on the height of the child content. Which depends on the height on the parent. Argh! etc.

So you have to give its parent a percentage height. And the parent's parent, all the way up to the root. Example doc:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head>
    <style type="text/css">
        html, body { margin: 0; padding: 0; }
        html, body, #mything, #mything textarea { height: 100%; }
    <div id="mything">
        <textarea rows="10" cols="40">x</textarea>

The other possibility if you don't want to have to set height on everything is to use absolute positioning. This changes the element that dimensions are based on from the direct parent to the nearest ancestor with a ‘position’ setting other than default ‘static’. If there are no ancestor elements with positioning, then dimensions are based on the “Initial Containing Block”, which is the same size as the viewport.

Finally, there's the trivial problem of ‘100%’ being slightly too big because of the additional padding and border applied to textareas. You can work around this by:

  • compromising on something like 95%, or
  • setting padding and border to 0/none on the textarea, or
  • using “box-sizing: border-box;” to change what ‘height’ means. This is a CSS future soup feature which requires many additional browser-specific restatements (such as ‘-moz-box-sizing’).