theme scroll bars

nord-polar-night-aurora.scss

 $ui-fold-arrows-color     : $ui-foreground;
 
 // rstudio
-$ui-rstudio-background         : darken($ui-background, 2%);
-$ui-rstudio-color              : $ui-foreground;
-$ui-rstudio-tabs-inactive      : $nord1;
-$ui-rstudio-tabs-inactive-color: transparentize($ui-foreground, 0.4);
-$ui-rstudio-tabs-selected      : $nord2;
-$ui-rstudio-tabs-selected-color: $nord5;
-$ui-rstudio-toolbar            : $ui-rstudio-tabs-selected;
-$ui-rstudio-search             : $ui-rstudio-toolbar;
-$ui-completions-background     : $ui-background;
-$ui-completions-color          : $ui-foreground;
-$ui-completions-border         : $ui-bracket;
+$ui-rstudio-background          : darken($ui-background, 2%);
+$ui-rstudio-color               : $ui-foreground;
+$ui-rstudio-tabs-inactive       : $nord1;
+$ui-rstudio-tabs-inactive-color : transparentize($ui-foreground, 0.4);
+$ui-rstudio-tabs-selected       : $nord2;
+$ui-rstudio-tabs-selected-color : $nord5;
+$ui-rstudio-toolbar             : $ui-rstudio-tabs-selected;
+$ui-rstudio-search              : $ui-rstudio-toolbar;
+$ui-completions-background      : $ui-background;
+$ui-completions-color           : $ui-foreground;
+$ui-completions-border          : $ui-bracket;
+$ui-rstudio-scrollbar-background: $ui-background;
+$ui-rstudio-scrollbar-handle    : $ui-code-chunk-background;
 
 // R language colors
 $rlang-comment  : transparentize($ui-foreground, 0.5);

oceanic-plus.scss

-/* rs-theme-name: Oceanic Plus SCSS */
+/* rs-theme-name: Oceanic Plus (SCSS) */
 /* rs-theme-is-dark: TRUE */
 
 @import "palettes/_oceanic-plus";
 $ui-fold-arrows-color     : $ui-foreground;
 
 // rstudio
-$ui-rstudio-background         : $base01;
-$ui-rstudio-color              : $ui-foreground;
-$ui-rstudio-tabs-inactive      : $base01;
-$ui-rstudio-tabs-inactive-color: $base04;
-$ui-rstudio-tabs-selected      : $base02;
-$ui-rstudio-tabs-selected-color: $base07;
-$ui-rstudio-toolbar            : $ui-rstudio-tabs-selected;
-$ui-rstudio-search             : $ui-rstudio-toolbar;
-$ui-completions-background     : $ui-background;
-$ui-completions-color          : $ui-foreground;
-$ui-completions-border         : $ui-bracket;
+$ui-rstudio-background          : $base01;
+$ui-rstudio-color               : $ui-foreground;
+$ui-rstudio-tabs-inactive       : $base01;
+$ui-rstudio-tabs-inactive-color : $base04;
+$ui-rstudio-tabs-selected       : $base02;
+$ui-rstudio-tabs-selected-color : $base07;
+$ui-rstudio-toolbar             : $ui-rstudio-tabs-selected;
+$ui-rstudio-search              : $ui-rstudio-toolbar;
+$ui-completions-background      : $ui-background;
+$ui-completions-color           : $ui-foreground;
+$ui-completions-border          : $ui-bracket;
+$ui-rstudio-scrollbar-background: $ui-background;
+$ui-rstudio-scrollbar-handle    : $ui-code-chunk-background;
 
 // R language colors
 $rlang-comment  : $base04;

rsthemes/nord-polar-night-aurora.rstheme

   border: solid 1px #46597c;
 }
 
+/* scrollbars */
+.rstudio-themes-flat .rstudio-themes-dark-grey .gwt-TabLayoutPanelTabs,
+.rstudio-themes-flat .rstudio-themes-dark-grey .rstheme_minimizedWindowObject .rstheme_center,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-track,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-corner,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-track,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-corner,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-track,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-corner {
+  background: #2e3440;
+}
+
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-thumb,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-thumb,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-thumb {
+  background: #3b4252;
+  border: 4px solid #2e3440;
+}
+
 .terminal {
   background-color: #2e3440;
   color: #d8dee9;

rsthemes/oceanic-plus.rstheme

-/* rs-theme-name: Oceanic Plus SCSS */
+/* rs-theme-name: Oceanic Plus (SCSS) */
 /* rs-theme-is-dark: TRUE */
 /* https://github.com/marcoms/oceanic-plus */
 .ace_gutter {
   border: solid 1px #4F5B66;
 }
 
+/* scrollbars */
+.rstudio-themes-flat .rstudio-themes-dark-grey .gwt-TabLayoutPanelTabs,
+.rstudio-themes-flat .rstudio-themes-dark-grey .rstheme_minimizedWindowObject .rstheme_center,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-track,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-corner,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-track,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-corner,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-track,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-corner {
+  background: #1B2B34;
+}
+
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-thumb,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-thumb,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-thumb {
+  background: #343D46;
+  border: 4px solid #1B2B34;
+}
+
 .terminal {
   background-color: #1B2B34;
   color: #D8DEE9;

rstudio/_rstudio-dark.scss

   	background: $ui-completions-background !important;
   	border: solid 1px $ui-completions-border;
   }
-}
+}
+
+/* scrollbars */
+.rstudio-themes-flat .rstudio-themes-dark-grey .gwt-TabLayoutPanelTabs,
+.rstudio-themes-flat .rstudio-themes-dark-grey .rstheme_minimizedWindowObject .rstheme_center,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-track,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-corner,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-track,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-corner,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-track,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-corner {
+  background: $ui-rstudio-scrollbar-background;
+}
+
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars ::-webkit-scrollbar-thumb,
+.rstudio-themes-flat .rstudio-themes-dark.rstudio-themes-scrollbars::-webkit-scrollbar-thumb,
+.rstudio-themes-flat.rstudio-themes-dark-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-thumb {
+  background: $ui-rstudio-scrollbar-handle;
+  border: 4px solid $ui-rstudio-scrollbar-background;
+}