There are three different themes to choose from:
If you click on the Menu icon in the upper right corner (), below the list of categories it will show the three themes with an asterisk by whichever one is currently enabled. Try them all to see which one works better. I was using the dark theme, but now I’ve switched to the CA theme. I think I’d still like to see one that is darker than the CA theme, but lighter than the dark theme. But both of them are bearable to me. I won’t be using the default theme, though. Too bright for me.