Removing 'Title Background' on homepage slider

Hi,
I’m using the MK theme for my website. I don’t want to have any titles on the homepage slider. I can remove the titles, but the background for the Slide 1 Btn Text remains. Looking at other comments in the forum, I added the following to style.css –
#slides article a.btn{
display: none!important;
}
But the background colour is still there. Does this code have to go somewhere in particular?

Please advise. Thank you.