How do I Limit Product Excerpts on Foster Template?

Site URL: https://www.thephotographicforecast.com

Hello, I'm trying to reduce the amount of characters when using a summary block and including product excerpts.

I've written details about the products in the initial product info area rather than the 'Additional Information' section due to the layout and use of images.

Now when using a summary block and opting to 'show excerpt', it shows the entire product description.

Is there a way to add custom CSS to change how much text is shown?

Thanks so much for any help!

Lisa