I was building custom elements with Polymer the other day, and I thought it would be cool to include Font Awesome for some sweet icon goodness. Everything was going great, until I switched over to Canary to check my work.

Busted Polymer Fonts

uh oh...

At first, I was pretty confused. Why was everything working fine in Chrome, but acting crazy in Canary? I did some digging and manged to turn up this thread on the Polymer mailing list.

The Fix

I had a bit of an "aha moment" when I remembered that the current version of Chrome doesn't actually hide any styles in the Shadow DOM, so my @font-face rules were ending up in the global scope. Canary, on the other hand, is encapsulating those styles in a shadow boundary and falling prey to an apparent bug.

update: All versions of Chrome now fully support style scoping with Shadow DOM

A simple workaround is to pull your @font-face rules out of the stylesheet for your element, and move them to the top of your import, like so:

  @font-face {
    font-family: 'FontAwesome';
    src: url('../fonts/fontawesome-webfont.eot?v=4.0.3');
    src: url('../fonts/fontawesome-webfont.eot?#iefix&v=4.0.3') format('embedded-opentype'), url('../fonts/fontawesome-webfont.woff?v=4.0.3') format('woff'), url('../fonts/fontawesome-webfont.ttf?v=4.0.3') format('truetype'), url('../fonts/fontawesome-webfont.svg?v=4.0.3#fontawesomeregular') format('svg');
    font-weight: normal;
    font-style: normal;

<polymer-element name="semantic-ui-icon" noscript>
    <link rel="stylesheet" href="./icon.css">

I found this approach in the Polymer documentation, so I'm hoping it's considered a best practice. You'll also need to do this if you're using @-webkit-keyframes rules.

I hope that clears things up for some of you who may have been stuck. I know it took me a couple days to come up with this solution, so I thought it best to go ahead and post about it :)