Popcode renders in unusable state in Safari 8

[alexpelan]

Describe the bug
In Safari 8, Popcode renders incorrectly and is not interactive

To Reproduce
Steps to reproduce the behavior:

1. Go to popcode.org

Expected behavior
Popcode will work - you can write code and the preview will appear

Screenshots

Desktop (please complete the following information):

• OS: Mac OS Yosemite
• Browser Safari
• Version 8

Additional context
On Browserstack, not on an actual device