Picking a framework

Hi everybody. I am a video game programmer who got his start learning Python on this very site about 5 years ago now. I am back and want to develop a portfolio webpage to host and show my previous projects. I know a little bit of HTML and CSS (enough to get by) and rusty Javascript skills. I now mainly program in Java and C# now. What sort of web development framework would be best to learn? (I am also looking for it to be able to scale to mobile devices as well although I’d hope most frameworks make this smooth).