force featured image to be smaller

I am upgrading to version 2 and now so much of the customizations I did for version 1 are lost. I appreciate your hard work on version 2, but I don’t understand why so many of the tags had to change, making much of my custom css obsolete. Right now, I am trying to set the images on the details page to be no more than 300 px wide, for example. I set the size to medium in the gd images shortcode but that does not do the trick. Under version 1, this worked:
.gd_place img {
max-width: 300px !important;
}

How can I force the images to be smaller and remove the extra space between the image container and the profile info.
Thanks for your help.