Featured Image Borders Causing Problems – Please Help

I am using the twentyten theme with child themes.

https://todaysbighit.net78.net/wordpress/

I added borders around the featured images, but it added a border to the header image also.

How do I remove the header image border?

Adding this to the bottom of the style.css is the cause:

a img {
border: 1px solid #AAA;
padding: 6px;
background: white;
}

Without that code I lose the borders around the featured images.

Is there a way to exclude the header image from receiving that image?

(Second question)
How do I add the same hover property to the borders of the featured images that I have on regular images on the homepage containing a link?