How do I do that? Can I?
It works the same way as creating formatting presets in 2.x. Select some text that uses the formatting you want for the style, then go to Format > Style > New Style from Selection.
All the best,
Keith
Create/highlight a word, give it the character attributes you want for that style, go to Format > Style > New Style from Selection… In the dialog that opens, give it a name, create a shortcut if desired, click the selector up-down carets where it says “Save all formatting” and from the dropdown choose “Save character attributes”, click “OK”. You can put a box round and/or a colour background to anything in that style if you wish.
Job done. 
Mark
EDIT: Keith got there first without the verbosity! 
Wait, I can just draw a box around rather than color fill? Another recent mention of this sent me back to check out style highlighting and I concluded it couldn’t be done box only – just color fill.
What is the secret?
gr
p.s. I promise to feel bad later if I should know this and have just forgotten.
Can’t you do it by just selecting the colour to be the background colour of the page? (Easiest way: use the colour dropper to click on the page.)
Well, that is still just a color fill, of course. The limitation of that would be that you can only play that game once. I had the impression from this and another post elsewhere that one could pick a box outline color instead of (just) a box fill. This holds promise for me since you could establish different outline colors for different styles.*
-gr
- In fact, my own dream (though you can’t quite do it) would be the ability to do this with a set of “null” styles – i.e. ones that didn’t change anything typographically, but just gave me the ability to visually box the text – useful for various purposes.