my yahoo emails suddenly are super small font. Im not sure what I did but I can't get it returned to the correct size

Hello nbssmith.

Thank you for using Apple Support Communities and for sharing these details with us. It sounds like you're experiencing issues with font size when checking your emails. If so, we'd like to assist in any way we can or point you in the right direction for help.

To confirm, are you using the Mail app to check your emails? If so, you can change and adjust your font size for the Mail app by selecting Format > Show Fonts. This will open the Font menu for the Mail app and you can adjust the size:

Change Fonts & Colors preferences in Mail on Mac - Apple Support

If you're using Safari to check your emails, the following resource can help:

Zoom in on webpages in Safari on Mac - Apple Support

We hope this information is useful. Cheers.