Vantage Featured Image thumbnail resizing problem

Hi,

I’ve already had most of my problem solved by another (closed) thread but haven’t quite gotten it sorted out:

Like the original poster, I’d like to have a thumbnail of the featured image from each of my posts appear to the left of the excerpts on my front page.

I’ve added the CSS and increased the thumbnail size to 300 x 200 in the Media Settings window and now have the small icon to the left. However, when I try to resize it by changing the CSS from “width: 11.68%” to, say 30%, the image becomes blurry as if being upscaled.

I’m still trying to understand how the the Media Settings work so there’s a good chance I messed something up there.

Any ideas about where I’m failing or an explanation of the specific media settings to tweak would be much appreciated.

Thanks a lot.