"Select isn't broken." If you're working on a CSS file, and none of your changes are being applied, check for typos, crashed servers, misplaced files, etc. Once you've ruled out simple mistakes, you might have a syntax error like this:
.klass {
opacity: 0.5;
};The trailing semicolon is incorrect, and none of the CSS below it can be understood by the browser.
Change this to:
.klass {
opacity: 0.5;
}There may be some environments where a broken CSS file fails loudly; Code Sandbox or Codepens are not among them. If you're changing CSS and nothing is happening, start looking for syntax errors.