DevTools: prettify Ctrl-O dialog

These are minor changese to Ctrl-O dialog styling so that it is better
visible over the text editor.

TBR=pfeldman
NOTRY=true

Review URL: https://codereview.chromium.org/441613004

git-svn-id: svn://svn.chromium.org/blink/trunk@179484 bbb929c8-8fbe-4397-9dbb-9b2b20218538