font size and color

I am brand new to blogging and am not very computer savvy – definitely don’t understand all these technical terms. Because of this, I chose one of the themes offered for my blog. However, I would like to change the color and size of the font as well as the size of the pictures. I’ve attempted to follow directions that I’ve seen by putting code (or whatever) in the CSS edit section of the blog, but I cannot seem to get anything to change. My blog is:

https://sewing-adventures.com

Do the theme templates not allow these kind of changes? If I can change font size/color, could someone please let me know – in very simple terms, if possible – how to make this happen.

Thanks so much!

Kathy