Keep Aspect Ratio With HTML and CSS

When working on my javascript colorpicker, one of the things I thought would be really cool is if you could resize it and have the colorpicker automatically respond to different widths. When I first made it, I had basically defined static widths with the thought that there could be different themes (small, normal, large) which defined different widths.

This turned out to be a pain, since you had to manually figure out what each width needed to be for the total size. To complicate things further, I wanted to have a different percentage width when accessing the colorpicker via an iPhone. I found that the hue slider was a little too small to accurately slide with the touch interface, so I wanted it to take up more of a percentage of the total width. I’m can be lazy about calculating widths in CSS, so I went off looking for a different way to do this.

Aspect Ratios

Why couldn’t I just use percentage widths? Because the left portion of the colorpicker needs to be a square - or else the gradients for saturation and value just look weird and don’t really map up 1:1. I did some searching and found a CSS workaround to keep the aspect ratio of a fluid element by ansciath. The meat of this trick is that according to the spec for margin-top, a percentage refers to the width of the containing block, not the height. This post got me much of the way there, but I had to include a couple of fixes for IE and ways.

The really nice part about using this technique is that it makes spectrum extremely easy to skin in your own CSS. Check out ColorStash for an example of this. Using media queries and max-widths, I can change the width of the colorpicker as the browser resizes to get some really responsive behavior on a UI control (colorpicker) that has typically been very static.


See the demo of the aspect ratio and media query. Try resizing your browser window to under 480px width to see the switch happen. Here is the full source code for the demo.

Below is a snippet showing the basic HTML/CSS needed for this technique:

<div class='container'>
    <div class='outer'>
        <div class='fill'></div>
        <div class='inner-top'>
            <div class='square'>Always a square</div>
            <div class='right'>% width</div>
    <div class='bottom'>
.outer {
  width: 100%;
.inner-top {
   position:absolute; top:; left:; bottom:; right:;
.square {
    position: absolute;
.right {
    position: absolute;
    background: purple;
.fill {
    *height: 80%;
    margin-top: 80%;  /* Same as square width */
@media (max-width: 480px) {
    .square { right: 51%; background: blue; }
    .right { left: 51%; }
    .fill { margin-top: 49%; }


  1. Happy Frog Media Says:

    Very informative, thanks for sharing this

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