My answer to #1: It should be added the css file applied to the page. I looked a bit inside the theme, there were no instructions on how to modify the css files. From what I was able to understand, depending on the theme that you have chosen in the config file like this:
inverse = false # indicating if the theme should use inversed colors
name = "cerulean" # name of the theme to use
a different css file will be used. In this case it will be cerulean.css. All css files are in /hugo-multi-bootswatch/static/css/theme/. But there is also an empty css file in the theme /hugo-multi-bootswatch/static/css/style.css. Look inside your generated pages and see if this file is being used. If so, you can try adding the following to the css file:
I assume this empty css file was created to override properties.