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

/***********
 ! Scrollbar
************/

@include exports("scrollbar") {
    scrollbar {
        $_slider_min_length: 40px;
        $_slider_normal_width: 7px;
        $_slider_small_width: 4px;

        // disable steppers
        @at-root * {
            -GtkScrollbar-has-backward-stepper: false;
            -GtkScrollbar-has-forward-stepper: false;
        }

        background-color: $scrollbar_bg_color;
        transition: 300ms ease-out;

        // scrollbar border on the content side
        &.top { border-bottom: 1px solid $borders_color; }
        &.bottom { border-top: 1px solid $borders_color; }
        &.left { border-right: 1px solid $borders_color; }
        &.right { border-left: 1px solid $borders_color; }

        &:backdrop {
            background-color: $backdrop_scrollbar_bg_color;
            border-color: $backdrop_borders_color;
            transition: 400ms ease-in;
        }

        slider {
            min-width: $_slider_normal_width;
            min-height: $_slider_normal_width;
            border: 1px solid transparent;
            border-radius: $roundness;
            background-clip: padding-box;
            background-color: $scrollbar_slider_color;

            &:hover { background-color: $scrollbar_slider_hover_color; }
            &:hover:active { background-color: $scrollbar_slider_active_color; }
            &:backdrop { background-color: $backdrop_scrollbar_slider_color; }
            &:disabled { background-color: transparent; }
        }

        &.horizontal slider { min-width: $_slider_min_length; }
        &.vertical slider { min-height: $_slider_min_length; }

        &.fine-tune slider:active {
            background-color: lighten($scrollbar_slider_active_color, 10%);
        }

        &.overlay-indicator {
            opacity: .8;

            &:not(.dragging):not(.hovering) {
                border-color: transparent;
                opacity: .4;
                background-color: transparent;

                slider {
                    min-width: $_slider_small_width;
                    min-height: $_slider_small_width;
                    background-color: $fg_color;
                    border: 1px solid if($variant == "light", white, black);
                }

                // hide steppers
                button {
                    min-width: $_slider_small_width;
                    min-height: $_slider_small_width;
                    border-color: transparent;
                    -gtk-icon-source: none;
                }

                &.horizontal {
                    slider { min-width: $_slider_min_length; }
                    button { min-width: $_slider_normal_width; }
                }

                &.vertical {
                    slider { min-height: $_slider_min_length; }
                    button { min-height: $_slider_normal_width; }
                }
            }
        }

        // stepper styling
        button {
            min-width: $_slider_normal_width;
            min-height: $_slider_normal_width;
            padding: 0;
            border: 0;
            border-radius: 0;
            border-color: $borders_color; // FIXME overwritten by global button definition
            background-color: transparent;
            box-shadow: none;
            color: $scrollbar_slider_color;

            &:hover { color: $scrollbar_slider_hover_color; }
            &:active, &:checked { color: $scrollbar_slider_active_color; }
            &:backdrop { color: $backdrop_scrollbar_slider_color; }
        }

        // button icons
        &.vertical {
            button {
                &.down {
                    -gtk-icon-source: -gtk-icontheme("pan-down-symbolic");
                    border-top: 1px solid $borders_color;
                }

                &.up {
                    -gtk-icon-source: -gtk-icontheme("pan-up-symbolic");
                    border-bottom: 1px solid $borders_color;
                }
            }
        }

        &.horizontal {
            button {
                &.down {
                    -gtk-icon-source: -gtk-icontheme("pan-right-symbolic");
                    border-left: 1px solid $borders_color;
                }

                &.up {
                    -gtk-icon-source: -gtk-icontheme("pan-left-symbolic");
                    border-right: 1px solid $borders_color;
                }
            }
        }
    }
}