How to Use a custom font for the Site Title

Site URL: https://www.tallsclothing.com/

Hi for my website I am currently using the tresoire template and I have been trying many different css code options for changing the font of the site title and none of them are working. I got other parts of my sight working with the custom font but not the site title. Can anyone help me with this? Also how would I go about changing the fonts for the pages that are at the top of my site?

Add to Home > Design > Custom CSS

@font-face { 
  font-family: nexa; 
  src: url(https://static1.squarespace.com/static/5d2b34d977f80900014edb0d/t/5e3f7cb899dd6e23d8b1e836/1581219002767/nexa-regular.otf); 
} 
a#site-title {
    font-family: nexa;
}