There is a subliminal point to what you say. Black backgrounds with red text are associated with things like spam, viruses, and websites under construction. Black is OK with borders but the page should have colors either associated with the US flag and white or black text or use pastel backgrounds with black text. Check out go fund me as an example too.
Correct, they are using CSS with lots of inheritance, important attributes, and overriding. Styling sucks and why I just use inline because I always know exactly what is happening at each node. It is harder to read, but then again, who reads it anyways except a dev? That is a nice shade of blue but then the red text becomes to glaring and would have to be made into a maroon color.
Here is how it works.
#RRGGBB or #RGB
Where r,g,b is red, green, blue and each value of r g or b can be 0-9 or A-F to represent the numbers 10-16.
So #FF0000 is red and so is #FF