variable work margins

[queerty]

I currently have my custom site skin (using the wizard) set to 25% for work margin width. this is perfect when I am reading on the computer seeing as it sets it on par with the reader mode, but allows me to use the color scheme I want. it's absolutely awful when I read on mobile, however, as it cuts each line down to 2-6 words. is there some CSS I could stick on the skin so that the margins are 25% on my computer, but use the default 0% margin settings while on mobile?