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

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

@include exports("scrollbar") {
    scrollbar {
        $_slider_min_length: 20px;

        // 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
        &.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
        slider {
            min-width: 7px;
            min-height: 7px;
            margin: -2px;
            border: 4px 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; }
        }

        &.fine-tune {
            slider {
                min-width: 7px;
                min-height: 7px;
            }

            &.horizontal slider { border-width: 1px; }
            &.vertical slider { border-width: 1px; }
        }

        &.overlay-indicator {
            &:not(.dragging):not(.hovering) {
                border-color: transparent;
                opacity: 0.4;
                background-color: transparent;

                slider {
                    margin: 0;
                    min-width: 5px;
                    min-height: 5px;
                    background-color: $fg_color;
                    border: 1px solid if($variant == 'light', white, black);
                }

                button {
                    min-width: 5px;
                    min-height: 5px;
                    background-color: $fg_color;
                    background-clip: padding-box;
                    border-radius: $roundness;
                    border: 1px solid if($variant == 'light', white, black);
                    -gtk-icon-source: none;
                }

                &.horizontal {
                    slider {
                        margin: 0 2px;
                        min-width: $_slider_min_length;
                    }

                    button {
                        margin: 1px 2px;
                        min-width: 5px;
                    }
                }

                &.vertical {
                    slider {
                        margin: 2px 0;
                        min-height: $_slider_min_length;
                    }

                    button {
                        margin: 2px 1px;
                        min-height: 5px;
                    }
                }
            }

            &.dragging,
            &.hovering { opacity: 0.8; }
        }

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

        &.vertical slider { min-height: $_slider_min_length; }
        // button styling
        button {
            padding: 0;
            min-width: 7px;
            min-height: 7px;
            border-style: none;
            border-radius: $roundness;
            transition-property: min-height, min-width, color;

            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'); }

                &.up { -gtk-icon-source: -gtk-icontheme('pan-up-symbolic'); }
            }
        }

        &.horizontal {
            button {
                &.down { -gtk-icon-source: -gtk-icontheme('pan-right-symbolic'); }

                &.up { -gtk-icon-source: -gtk-icontheme('pan-left-symbolic'); }
            }
        }
    }

    treeview ~ scrollbar.vertical {
        border-top: 1px solid $borders_color;
        margin-top: -1px;
    }
}