I decided I want to show thumbnails on the front page excerpts, so I'm using Thumbnail for Excerpts plugin. It works really well. You have to edit the code to change things, and it gives you the CSS class. I thought I could go into theme options and style the class so the thumbnails would have a 1px black border, but it's not showing up that way. I used this:

imgtfe {
border: solid 1px #000000;
}

imgtfe is the class. The thumbnails are small, 65px high. I wonder if something that small is by default not "allowed" to have a border?

A dot is missing

.imgtfe {
border: solid 1px #000000;
}

or, to limit it to images with that class, in case there are other elements with the class imgtfe, too

img.imgtfe {
border: solid 1px #000000;
}

I usually add the selector (img, div, span, p) etc. too, to make things clearer:
div.classname instead of .classname

dot means class
hash means ID

.classname or img.classname
#idname or img#idname

Oh thank you again. Those dots'll get you every time.