Give <main> a definite flex basis (fixes #112)
Give <main> a definite flex basis (fixes #112)

The flexbox spec changed, so that if we want #editor and #result to cover 60 %
and 40 % of the code box, we need to give their parent a size that can be
determined without measuring content.

Chromium has already updated their implementation, making the Playpen really
annoying to use, and Firefox will update theirs eventually.
plietar/pony-playpen,plietar/pony-playpen,rust-lang/rust-playpen,rust-lang/rust-playpen,tilpner/rust-playpen,tilpner/rust-playpen,rust-lang/rust-playpen,tilpner/rust-playpen,tilpner/rust-playpen,plietar/pony-playpen,rust-lang/rust-playpen,plietar/pony-playpen