Add border to teaser?

Hi,

I am struggling to add a border to my article teasers.

I just want to be able to show a more definitive separation between teasers.

I may not wish to add a border for EVERY teaser, just per content type.

In node.css I tried:

.node .node-article .node-teaser {
border: 1px;
border-bottom-color:#CCCCCC;
}

also

.node-article .node-teaser {
border: 1px;
border-bottom-color:#CCCCCC;
}

......but to no avail :/

Can somebody help please.

Thanks.

Shaun