Another problem I ran into when building my first mobile game (using HTML, CSS and JS) was that while testing it on my phone I found my graphics were all blurred. Quite obvious that it was because my phone has a high pixel density screen as many do now. However, my graphics are pretty much all applied as CSS background images and I had not had to deal with this issue before in anything other than images. A Google search and Stack Overflow provided the answers I needed though.
I recently used Telerik Platform (http://www.telerik.com/platform) to build my first mobile game (Wah! http://www.ampzone.com/projects/wah). It was a bit of an experiment as I didn't know how well a game built with HTML, CSS and JS would work out on a mobile device. While I feel I have plenty of room for improvement, overall I think the test proved a success. I'm just going to write about one issue I had while attempting to improve the performance of the animations in my game.