It looks like line 2,309 of your default.css file in your BuddyBoss theme is the culprit. It is actually assigning bottom and left margin in addition to the 7px top margin to the images.
Normally you would be able to add a line at the bottom of the default.css file in the theme that overrides the margin settings just for the slider, like this:
#content .promo_slider img { margin:0; }
However, the theme is using an !important
tag, which will have to be removed for this to work. You should be able to find it on line 2,309. Just change it from this:
margin: 7px 15px 10px 0 !important;
to this:
margin: 7px 15px 10px 0;
You actually won’t have to add the initial line specific to the promotion slider since line 2,329 will kick in and set the margin to zero for you.
I am not sure where else in your theme you may see the effect, but it is a very bad practice for a theme to use the !important
tag.