I usually don't like the default font in any theme. I put this html code in many posts:
At the top of the post:
<div style="font-family:georgia; font-size:medium; color:black;">
You can use size:large or small or x-large or x-small, even xx I think.
Georgia is a nice, readable font.
I cannot for the life of me get my head around this trend to use gray text (like right here). I only have human eyes. They don't do stuff that is solely machine-readable.
At the very bottom of the post:
to end the div.
NOTE: Either put this code in at the very start before you create the post, or wait until you're finished, then add it. Depending on your theme it may behave better one way than the other, in that it may cause some trouble with paragraph and line breaks. So experiment before committing!
If you create the post before adding the code, first copy the post to another temporary one before introducing the custom HTML code. I love backups! In the biz they used to call me the The Backup King.
Don't mean to insult anyone who already knows this. And I'll greatly appreciate anyone offering a better way! (Now that we all have to become HTML coders.)
Now back to outdoor earthen reality, where I am a much better person.