If you have special CSS that you want in your website but none of the existing tags under Style Settings suit, then search for USER.SETTINGS.CSSLARGE and place your CSS there.
Then refer to it by class. For example, in this website we have added CSS for blinking text (we certainly do not recommend blinking text - it's just an example), and referred to it via the class blink...
This is an example of blinking text on a large device using the largeblink class.
large device blink.
But this text doesn't blink on a small device. So search for USER.SETTINGS.CSSSMALL and place the same CSS there.
This is an example of blinking text on a small device using the smallblink class.
small device blink.