Margins slideshow block

I’m wondering if someone can help me setting the margins of a block on my website. I created a slideshow with MetaSlider Plugin Version 3.20.2. Then I pasted the shortcode on my page and I tried to set the margins as I intended.

I pretend to remove the left and right margin as well as the top margin in order to put the slideshow block full width and without white space between the block and the header of my website.

I tried with CSS code but I’m a beginner. I created a class in CSS additional with several different codes and then I associated it with the block but none of them worked as I intend.

Can someone please help me? Thank you!