Hi Dave!
You are doing well so far. One possible solution that I implemented in order to change the background color of the selected option was to first implement them as a set of radio buttons.
I then added the property appearance: none
to the radio inputs themselves in order to hide the default styles. I selected the label
of the adjacent selected radio button with the pseudo selector :checked
like so .radio-input:checked + label
and altered the background of the label itelf. Now whichever radio input is checked will have the background color you set.