How to set background highlight for certain strings? (YAML/Sublime Text 3 themes)

Hi! I have created a custom theme and syntax highlighting for linguistic purposes that work very well — they change text color according to rather complex regexes.

However, I want to change the background color for given strings — any two or more spaces, to be exact. How to do it?

I am talking about such effect: http://imgur.com/a/gwftx