Feel free to look up the referenced CSS selectors & properties at MDN (the link is on the right side of this page).
Selectors
To create an accordian, you’ll need to view this presentation & look for the following selectors:
::before:checked:last-of-type~ combinator
CSS Building Blocks: Selectors
Properties
To create an accordian, you’ll need to view this presentation & look for the following CSS properties:
contentcursor(I don’t cover this in any presentation, so look it up)list-styletransform: rotate
CSS Building Blocks: Selectors
Find content in the section on ::before & ::after:
Tables & Lists: Organized Data
Find list-style in the section on Lists:
Decorating with CSS: Cool Ways to Make Things Pretty
Find transform: rotate in the section on transform (it’s in the example code):