How can I resize containers for optimized mobile viewing?

[whiskeymon]

Hello,

I need to resize the containers on my mobile website only. Videos, banners, etc looks great on desktop. When switching to mobile, the containers take up about 1/3 of the screen. I want to put in a cropped version of the desktop banners to fill up the entire height of the mobile screen. 

[whiskeymon]

This request would be for code to resize all sections and banners for mobile only while leaving desktop as is. Thank you.