Add this to custom scss file or page settings:
#g-navigation .g-main-nav .g-toplevel >li.active >.g-menu-item-container .g-menu-item-title {
border: none;
}
#g-navigation .g-main-nav .g-toplevel >li >.g-menu-item-container .g-menu-item-title {
border: none;
}
To add custom style sheet to Gantry 5 Framework please follow these instructions:
docs.gantry.org/gantry5/tutorials/adding-a-custom-style-sheet
or if you want to add them in the Page Settings:
docs.gantry.org/gantry5/configure/page-settings#custom-css-js