If a style sheet is wrong or missing
When you visit a webpage, Safari uses the Cascading Style Sheet (CSS) you specify in addition to any style sheets specified by the page. A style sheet specified by the page may override your style sheet.
To check that you have specified the correct style sheet:
Choose Action menu > Preferences and click Advanced. (The Action menu is near the upper-right corner of the Safari window, and looks like a gear.)
Check the “Style sheet” pop-up menu to see what style sheet is selected. For more information about the options, click the Help button (looks like a question mark).