1. add "no margin" and "no padding" block variations to the spacer and menu particle in the navigation section.
2. Use this code...
.g-slideshow .g-slideshow-slider .swiper-slide .slide {
background-size: contain;
}
3. add "no margin" and "no padding" block variations to the slider particle in the slideshow section.
To create a custom CSS compatible with Gantry 5 please read this
http://docs.gantry.org/gantry5/tutorials/adding-a-custom-style-sheet
.
Remember to recompile CSS from base outline too.
Regards, Mark.