yeah, the actual CSS doc you tweaked is probably the compile output from various sass style sheets. The sasss uses a variable, hopefully just set in one place and then called throughout. Then at some point before going to the production site, a preprocessor like gulp runs through and generates one single CSS document that shows the fixed value from the variables.
variables, functions and nested selectors make CSS so much easier on big projects once you start using them. I was resistant at first but it is very nice once you get into it on a regular basis.