html – The beginner's doubt – How to evaluate if the internet user will use the source on the site?

When the user has not installed the font given in the css file on his computer, the browser uses the font of the default style, based on the documents that I read.

Is there a site, portal or library used to protect against this risk? For example, you create a layout for a young audience, but as it is from a little-known source, the site ends in Times New Roman for most users.