[html] Why is my CSS style not being applied?

In addition to the solutions posted above, having gone through the exact same problem, make sure you check your HTML. More specifically whether you've properly labelled your elements, as well as class and id selectors. You can do this either manually or through a validator (https://validator.w3.org/).

For me, I missed the equal sign next to the class (<div class someDiv> vs <div class = "someDiv">, hence why no CSS property was applied.