Change search match style

@mlettini @starzonmyarmz @kenearley @stof @koenpunt

This is a relatively simple change. Rather than use a background color change to indicate a search match, we're now going to use an underline. This change allows search indication to happen even when the result is highlighted. I also just like it more.

This PR also includes a fix for an issue introduced by the SASS conversion by flipping the single/multiple style order.