I'm in the process of adding security certificates to all my sites, via Let's Encrypt in the cpanel. I'm having an issue with older Joomla sites with J51 templates showing as having mixed content. Searching the Page Source I find that urls to google fonts in style sheets are using http instead of https. Back when the site was made google was probably using http. Newer sites display these urls without showing the https: part of the address. The urls display as //fonts.googleapis.com... Is there some Custom CSS snippet I could add to the template to convert http to https?

An example is https://webnanny.net/ using Virtuoso. I installed the most recent version of Virtuoso just in case that might help but it didn't. Joomla version and extension versions are up to date. This site is not a crisis because it's my own and is long past its sell by date; just haven't had time to build a new one. Client sites come first.