@Ric-Molina we don't support that in the Listly WP plugin settings.
Do you have a need to change text size within the item description text selectively? There's no support in markdown for this.
The plugin inherits the font size for the body text from the page it's embedded. If you need to increase or decrease the font size for the body text in the embedded list, you could wrap the plugin code in a DIV and add styles to the DIV.
<div style="font-size: 14px">
... listly plugin code here...
We will also look into adding alternate font-size in the Listly WP plugin settings. This way it can inherit from the host page OR use the custom font size from the settings