All elements have a default background-color of transparent.
background-color
transparent
Difference between background-color: hsl(180, 90%, 35%); and background-color: hsl(180, 80%, 25%);:
background-color: hsl(180, 90%, 35%);
background-color: hsl(180, 80%, 25%);
The first color isn’t darker than the second color.
source