In your custom CSS, you have this rule:
.post,#comments,#pings,#no-comments,#comment-form,.widget{
box-shadow:none !important;
border-radius:0 !important
}
In general, you should avoid the use of !important whenever possible. It makes later changes (like in this situation) more difficult (i.e., that’s why the border-radius property you added for the Facebook widget isn’t working). If some rule isn’t working, then just make the selector more specific instead of adding !important.
So, first remove the !important clause from the border-radius property because you’re going to use the border-radius property to make the rounded corners. You should see the corners round on your Facebook widget. To make a more general rule for all widget, you can add this:
#sidebar .widget {
border-radius: 8px;
}
I just used the same value that you added for your Facebook widget.
For the widget titles, you can use this:
.widget-title {
border-radius: 8px;
margin-top: 0;
}
The margin-top of zero will eliminate the extra space at the top of the Category widget. The single value for border-radius rounds all four corners. If you want to have just the top corners rounded, use this instead:
.widget-title {
border-radius: 8px 8px 0 0;
margin-top: 0;
}
As far as the extra space at the bottom of the Facebook widget, that’s a bit more problematic. There’s an inline style which sets the height of the iframe to 400px (an iframe is like a window into another site, in this case, Facebook). To override this, you can add this CSS:
#facebook-likebox-2 iframe {
height: 250px !important;
}
Note that in this case, the use of the !important clause is necessary because that’s the only way to override an inline style (an inline style is one which is written directly into the element and not contained in an external file). As the the number of FB likes for your page grows, you’ll have to increase the height value accordingly.