Welcome to PRS+ and the world of CSS
As CSS already implies, C
heets, there are many possibilities to get the format you want.
In your example you are setting font-family for body.
If an embedded CSS forces font-family lets say for the p-tag you are out of luck.
Your best guess is to check the embedded CSS with Sigil, or flatten them with Calibre.
and also: when I power off the unit, it takes about 5 or 6 seconds (forever!) from the time I slide the power slider until it turns off. Is that normal? Powering on is normal (no lag).
A) on the setting for Standby-Screen
B) the current ebook-file
With some formats it will take a while to generate the standby image.
Though 5 seconds and more are rather long (for a x50, more often seen with 300/505)
Please try some other books and formats, too. (epub, pdf, lrf)