numix-gtk-theme/gtk-3.20/scss/widgets/_grid.scss

/******************
 ! Grid and flowbox
*******************/

@include exports("grid") {
    list {
        color: $text_color;
        background-color: $base_color;
        border-color: $borders_color;

        &:backdrop {
            background-color: $backdrop_base_color;
            border-color: $backdrop_borders_color;
        }

        row { padding: $spacing; }
    }

    row {
        transition: all 150ms cubic-bezier(0.25, 0.46, 0.45, 0.94);

        &:hover { transition: none; }

        &:backdrop { transition: 200ms ease-out; }

        &.activatable {
            &.has-open-popup, // this is for indicathing which row generated a popover see https://bugzilla.gnome.org/show_bug.cgi?id=754411

            &:hover { background-color: if(variant == light, transparentize($fg_color, .9), transparentize($fg_color, .95)); }

            &:active { box-shadow: inset 0 2px 2px -2px transparentize($black, .8); }

            &:backdrop:hover { background-color: transparent; }

            &:selected {
                &:active { box-shadow: inset 0 2px 3px -1px transparentize($black, .5); }

                &.has-open-popup,
                &:hover { background-color: mix($selected_bg_color, $fg_color, .1); }

                &:backdrop { background-color: $selected_bg_color; }
            }
        }

        &:selected { @extend %selected_items; }
    }

    flowbox {
        rubberband { @extend rubberband; }

        flowboxchild {
            padding: $spacing;
            border-radius: $roundness;

            &:selected {
                @extend %selected_items;

                outline-offset: -2px;
            }
        }
    }
}