How To Change Ishimoto Site Title Font Using CSS

I'm using the Ishimoto template. Having a hard time figuring out how I can change my site title font, i've gone through multiple threads on this forum and have been unsuccessful in finding a solution to the problem. The website is live but has a cover page right now for the under construction phase as i work to get it the way i want.

The code i was trying to use was

@font-face { font-family: 'GeosansLight'; src: url('https://static1.squarespace.com/static/5a8c34eb51a584a57bc62511/t/5a93aadff9619a83af6f6839/1519626975231/GeosansLight.ttf '); font-weight: normal; font-style: normal; } .has-site-title .Header-branding { font-family: "GeosansLight"; }