Version of CSS or Quirks?

Hi,

I know a bit about CSS but I’m still new with finding selectors and I really don’t know that much about different CSS versions. I was looking for a theme that is fairly new, simple, clean, and highly rated but also not too difficult to customize with CSS (as I’ve found that certain themes don’t always respond well).

I’m currently trying to set a transparent background for this theme for a majority of the sections, but this is one of the first themes I was able to find the selector but it doesn’t respond to the transparent element at all (I have a dark background image set, standard white foreground in content area, and black background just in case). However, the same CSS code will work with a color. For example, the code I’m using (tried in both CSS areas of the customizer) is:

div#content.site-content {
background-color: transparent;
}

The above code does not do anything, however if I change the color from “transparent” to purple” it changes the background color of the content area. Am I missing something?

Thanks in advance,
-Tom