Change syle of crossword

Hi, I am building a site for a crossword creator. I have uploaded one of his crosswords and it seems to be working fine.

I would like to change the style of the crossword so it is more in line with the website style, mainly the colours of the highighted box (yellow) and the highlighted and bordered text (red). I am able to change the text font and buttons but not these items. Is this possible?

The page I need help with: [log in to see the link]