Use this code...
#g-page-surround::before, #g-page-surround::after, #g-copyright::before, #g-copyright::after {
content: none;
}
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.