I am utilizing a wordpress with this http://pacelinegroup.com/

As you can tell at sidebar under sponsors there is a line that overlaps in the page. It is the grey line

I edited this part using inspect element and transformed the element.style to width:0px it labored and also the grey line vanished, but the truth is i dont understand how to get it done in wordpress. How do i edit that using css or whatever possible

I additionally attempted editing style.css in wordpress by using this

div.ngg.slideshow.widget

or

.div.ngg.slideshow.widget

Did not work either. Help me how you can fix this. Btw this really is nextgengallery