Square images in "last comments" to round images (I have the code but…)

Hi and thx Alx for your amazing theme.

My web is https://www.yourmedlife.com and I need to change the square images in the widget “last comments” to round images. I have the CSS code to do it:

border-radius: 200px 200px 200px 200px;
-moz-border-radius: 200px 200px 200px 200px;
-webkit-border-radius: 200px 200px 200px 200px;
border: 0px solid #000000;

However I test it in Tools Developer with Google Chrome but changes are applied to all images in the web.

Can somebody help me?

Thx!