Summary

By default, Confluence provides Times New Roman, Helvetica or Courier fonts for use. You can use your own fonts by declaring them in a @font-face CSS rule in your Stylesheet.

You can follow Styling Fonts in Confluence guide if you want to change from default Helvetica/Arial – sans serif

Solution

If you want to use your own custom fonts, you can do the following:

1. First you need to declare the new font using CSS @font-face.
   You can use fonts located on local network, web services, such as google or simply attach them to a Confluence page and point to that attachment in your declaration, just don't delete that page later accidentally (for example: http://confluence_url/download/attachments/65641/attachment-name.ttf)
   Here is a format for declaration

    @font-face {
       font-family: 'YourFontName'; /*a name to be used later*/
       src: url('http://domain.com/fonts/font.ttf'); /*URL to font*/
   }

    Here is an example of declaration for "Pirata One" font available on Google Fonts (https://fonts.google.com/specimen/Pirata+One

   @font-face {
     font-family: 'Pirata One';
     src: url(https://fonts.gstatic.com/s/pirataone/v15/I_urMpiDvgLdLh0fAtofhi-Orr3CZZ4.woff2);
   }

2. Next, you need to specify which elements the font will be applied to, you can refer to Styling Confluence with CSS
   

   .wiki-content,
   .wiki-content p,
   .wiki-content table,
   .wiki-content tr,
   .wiki-content td,
   .wiki-content th,
   .wiki-content ol,
   .wiki-content ul,
   .wiki-content li {
    font-family: Times, "Times New Roman", serif;
    font-size: 14px;
   }

3. Finally, you can put both together in Stylesheet, either for Confluence or just specific Space.
   Here is an example of earlier mentioned "Pirata One" font

   @font-face {
     font-family: 'Pirata One';
     src: url(https://fonts.gstatic.com/s/pirataone/v15/I_urMpiDvgLdLh0fAtofhi-Orr3CZZ4.woff2);
   }
   
   .wiki-content,
   .wiki-content p,
   .wiki-content table,
   .wiki-content tr,
   .wiki-content td,
   .wiki-content th,
   .wiki-content ol,
   .wiki-content ul,
   .wiki-content li {
   background-color: #fff !important; 
   font-family: 'Pirata One', serif;
   font-size: 14px; 
   }