Is there something funny about font size in the new "theme", or is it a problem at my end or what?
These days when I write/edit a post the preview looks the same as always. Then when I "save edit" the equations in the post suddenly appear much larger than they did in the preview... like inline equations are much larger than the surrounding text - not a big problem, just looks funny. (Look at this for example; here the $C$ in the first sentence is much larger than the C in the second sentence. Does it look that way to you as well?)
(Just checking whether the same problem appears here on meta: $x^2+y^2=1$. Nope, looks fine here.)