Adding Borders to a theme

Hi all,

Recently, I’ve been trying to add a white border around my portfolio images. As I’ve been searching around online I came to the conclusion to try this code to see how it works (honestly i have no CSS experience but I’m trying to learn quickly):

“.portfolio_image{
border: 1px solid #000;
width:198px;
}
.portfolio_image img{
width: 198px;
}”

When I put this code in, I put it in the edit css and the custom css tab under appearance (one is a plug-in, do i need both??). After i did that, none of my portfolio items displayed their front image or any of the other images once you click on it! The website I’m referring to is Knightsigns.ca.

Sorry if this needs more clarity! I appreciate any help

Thanks,
Phil