frontend/theme/trestle/theme/trestle/_navbar.scss
.app-sidebar-header {
.navbar-toggler {
background: $sidebar-mobile-toggle-bg;
border: $sidebar-mobile-toggle-border;
&:hover, &:focus {
background: $sidebar-mobile-toggle-active-bg;
border: $sidebar-mobile-toggle-active-border;
}
}
.navbar-toggler-icon {
background-image: $sidebar-mobile-toggle-icon-bg;
}
}