How to change font-size box author?

Hey there Tran,
I’m not sure which font you would like to change but this will change the widget fonts to a smaller size.

.widget-front {
font-size: smaller;
}

If you’d like to checkout all the font size possibilities id suggest going here: https://www.w3schools.com/cssref/pr_font_font-size.asp

If you’d like to change a specific font on your page find its class or element name and it should work fine. You can use Firebug or Google Chrome developers tools to inspect and find out the css you need to change to accomplish your goal.

To apply your css changes i suggest using a child theme https://codex.www.ads-software.com/Child_Themes

or a plugin such as Jetpack.

If you have any further questions please feel free to ask.