Create a CSS snippet with the following:
.callout {
font-family: "Some font", "Some alternative font";
font-size: 10em;
}
After creating the snippet, in vault/.obsidian/snippet/someCss.css, do remember to enable it in Settings > Appearances (CSS snippets) > someCss.
And your font should have been changed. In case you’re unsure on whether your CSS hits or not, change the font-size to some strange number. 10em should be very well seen.
If you can’t get it to display at a different size, make sure that your CSS file actually ends with .css, and is a plain text file. Not something made by Obsidian or a text editor like Word (or in some cases Text Edit (with formatting)).
So try this, and if it doesn’t work, please show a screenshot of your CSS file enabled in the Settings > Appearances (CSS Snippets), and post the CSS you tried.
Other variants can be used, and there is also a recent thread also discussing how to change the font:
Finally, this applies for the standard callouts of the following form:
> [!info]
> My info callout
If you’re using Admonition style callouts, they use a different syntax.