Remove default Supreme Directory background and Change colors of tiles(popular)

Hello,

I have two questions.

I am trying to use the CSS: ( background-image: url(“http://www.infermieriitalia.it/wp-content/themes/supreme-directory/images/featured.jpg”) !important; ) to remove the homepage default background image.

This CSS does not work for me when I add my custom URL in it, also does not work when I leave it in its current state such as it is above, the background image on website stays unchanged.
Help on this would be much appreciated.
Also to add, can I add more than one CSS code into the Scripts section GD>Design>Scripts?

And onto the less complicated topic, how do I change the color of the tiles shown on the home page under the search bar?

Would like to do this all on my own so I can learn and use this knowledge in the future. Please leave help on how to resolve my issues and hopefully this thread will be helpful for future GD users.

Help much appreciated

Best regards,
Nick