The Segoe UI font is not built into a browser. It is shipped with some Microsoft software. On a Mac, it is most probably not available, though a user might have acquired it separately or as part of some software package. You should remove the @font-face rule and the font files uploaded onto a server. Segoe UI is protected by copyright, and it must not be used as a web font without permission from the copyright holder, Microsoft (which probably won’t give a permission). You will need some other strategy, such as using another font either as the basic font or as a fallback font for visitors who don’t have Segoe UI in their systems.

Segoe Ui Regular Font

Segoe Font Download For Mac

The Open Sans is rather similar to Segoe UI, and it’s free (and it comes in 10 styles, including Book, Normal, Semi-Bold, Bold, and Extra-Bold weight).