header is overlapping new slider

i have installed metaslider, it works great but i wanted a full screen image so i google the heck out of it and found some CSS (not tech smart) and when i put it in the image went full size just great but the top part of the slider images is missing. its not cropped, its like its under the header. also i cant find a place to make my header space a little less height, its taking up too much room

please and thank you for any help

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