Hello,
Welcome to Microsoft Q&A
After testing, the title and description of a single setting item are {BodyTextBlockStyle} and {CaptionTextBlockStyle}.
Among them, the font color of the description is Gray (in Dark mode).
The code looks like this:
<StackPanel>
<TextBlock Style="{StaticResource BodyTextBlockStyle}" Text="System"/>
<TextBlock Style="{StaticResource CaptionTextBlockStyle}" Text="Display, sound, notifications, power" Foreground="Gray" Margin="0,1.5,0,0"/>
</StackPanel>
But in fact, the text styles provided by default are limited. You can flexibly create a variety of font styles according to your needs, in order to achieve a variety of typography.
If you want to know more about styles, you can check this document:
Thanks.