Thanks for your bug report. What OS are you experiencing this on? On Mac / Chrome 45 + 46 I'm seeing this:

ye on Mac 10.10.5 / Chrome 45.0.2454.99 (64-bit)
Thx. @sgomes or @surma can you try reproducing on your machines?
I'm having trouble with the links in the original issue, @addyosmani. How did you get to the preview?
I used the second link. The first Codepen is busted :)
The exact same code causes no issues in codepen. I'm currently investigating why, but I'd say the problem is something to do with runjs.cn
RunJS looks completely busted for me:

I see the same issues across all browsers in RunJS. I'm closing the bug because it seems apparent it's an issue with the site.
guys it's my fault, i apologize for the LINK about CodePen, in fact CodePen are working fine, but not work well on my own project and RUNJS. The other platform i didn't test.
thanks all of you in any way
closed .... but ..... but ... the picture are cut of form Chrome.
sadly face ( TAT ) @addyosmani
I had same trouble on Mac Chrome 46. I did 2 steps and had trouble.
.mdl-layout__drawer-button:before {
content: '';
}
sorry about my poor english skill too!
YES, i run my local project and in RUNJS both have same problem, but sgomes think it's RUNJS's is borken not MDL's problem, So he close this issues. i suggested that, build a new issue and link it to this issue. the present situation we were subject to,i completely think it is a bug.
是的呀,我本地测试和在runjs 上测试都是错了的,但sgomes 单单看了我runjs 上的例子就认为是 runjs 的问题... 所以呐,我建议你再开一个 issue 附带我这个链接,证明我们俩遇到了同样地问题。
This was an issue for me and @mwatanabe's workaround solved it for me.
I have this problem here today. So I decided to revive the topic.

It's funny because it happens to the customizer.

Ubuntu 14.04 / Chrome 49.0.2623.75 (64-bit)
Fixed in 1.2.1
I was experiencing exactly the same issue as the OP. Turned out I was missing <!doctype html>, which magically fixed the issue.
fixed my issue too.
CSS is the devil...
Thanks for sharing.
Most helpful comment
fixed my issue too.
CSS is the devil...
Thanks for sharing.