Hi Jeff!
If the CSS code is stored within the post content field within the database, it is basically treated as text on the database level, where the query is executed on. The database query cannot make a difference between useful and “irrelevant” text, therefore it matches that.
There might be a solution for this however. There is a secondary engine, the index table engine. It is basically tries to index the useful content on the pages – paragraph texts, titles etc.. and exclude all scripts, styles and other possibly irrelevant information.
This and this documentation chapters should include all the information you need, including video tutorials.
This should hopefully help eleminating some of the irrelevant content from the search.