How can I add a Google font that isn’t currently in the list of default fonts?
Hi @Garden_For_Wildlife and welcome to Community 
Sure, you should add this code to the Custom CSS field on the Appearance tab:
[class*='WidgetBackground__Container']{
font-family: Roboto;
}
Please note that the font you want to use should be installed to your website. Check it out and let me know if it helped 