According to Apple, you can change the colors of its Safari Web browser by using Cascading Style Sheets (CSS). Many websites offer free CSS templates for download (see Resources for some examples). You must have a CSS saved onto your computer before you can change the colors or style of your Safari browser.
Open the Safari web browser on your computer.
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Click the button that looks like a gear on the top right of the screen. This is the "Settings" button.
Click "Preferences," and you'll get a pop-up. Click "Advanced" on the top right of that pop-up.
From the drop-down menu labeled "Style Sheets," select "Other."
Browse through your computer and select the CSS template you want to use. Click "Open," then close the pop-up. The Safari colors and style will change to match the CSS template you selected.