Custom head tags

Custom meta tags and external CSS file tags can be added to your site in the Site settings > Template > Advanced tab > Custom head tags section.
 

Remote CSS link tags

An external CSS file may be included, for example, to use a remotely hosted font.  The tag should look something like so:

<link rel="stylesheet" type="text/css" href="https://example.com/file.css">
 

Custom meta tags

These can be any kind of meta tag you wish.  For example, if you sign-up for Google G Suite, you may need to use a special meta tag to verify you own the domain.

NOTE: You don't need to add meta tags hear for search optimization.  These can be set elsewhere.