CSS Update to Twitter Bootstrap

My site is: [login to view URL] - I'm currently using Twitter's bootstrap framework to style the site. I would like to make the following alteration, but in a separate CSS file that only affects the detail page. 1. I would like to alter the thumbnail and table to allow for a larger image - 300x200. However the corners are rounded and I would like to mask them over the image. 2. The bootstrap span is not 300 px wide, it's smaller (I think 298x189) - please make sure this size increase does not alter the grid or positioning of other elements on the page that are within the grid... ex. making the image wider, doesn't make other areas wider lower on the page. Please see the attached screenshot comparing what the new thumbnail would look like compared to the old. This should work on pages like: [login to view URL] [login to view URL] [login to view URL] Thanks.