Ask HN: In 2015, what do you use for the CSS of your web app?

Hi, I'm more of a JavaScript developer, doing mostly games (canvas) and applications where UI doesn't matter that much. But I will soon have to make the front end of a mobile web app. It features a lot of images, horizontal scrolling elements, and grid like display, and follow a designer's design. It has to be compatible with IOS and android webview from 4.2 (so no flexbox). What would you use? A framework like bootstrap or foundation, or sass directly...? I would like to avoid JavaScript as much as possible as it's a multiple page application.