tweak nord bracket

nord-snow-storm.scss

 // primary UI colors
 $ui-background           : lighten($nord6, 10%);
 $ui-foreground           : $nord3;
-$ui-code-chunk-background: $nord4;
+$ui-code-chunk-background: $nord6;
 $ui-selection            : transparentize($nord4, 0.6);
 $ui-cursor               : $nord12;
 $ui-cursor-normal-mode   : $ui-cursor;
 $ui-line-active-gutter    : $ui-background;
 $ui-line-active-selection : opacify($ui-selection, 1);
 $ui-line-find             : $ui-selection;
-$ui-bracket               : darken($ui-foreground, 50%);
+$ui-bracket               : darken($ui-background, 20%);
 $ui-invisible             : $nord4;
 $ui-indent-guide          : $nord4;
 $ui-debug-background      : lighten($ui-background, 10%);
 $ui-rstudio-color               : $ui-foreground;
 $ui-rstudio-tabs-inactive       : $nord4;
 $ui-rstudio-tabs-inactive-color : transparentize($ui-foreground, 0.4);
-$ui-rstudio-tabs-selected       : $nord5;
+$ui-rstudio-tabs-selected       : $nord6;
 $ui-rstudio-tabs-selected-color : $nord2;
 $ui-rstudio-toolbar             : $ui-rstudio-tabs-selected;
 $ui-rstudio-toolbar-color       : $ui-foreground;

rsthemes/nord-snow-storm.rstheme

 
 .ace_marker-layer .ace_bracket {
   margin: -1px 0 0 -1px;
-  border: 1px solid black;
+  border: 1px solid #cccccc;
 }
 
 .ace_marker-layer .ace_active-line {
 .ace_marker-layer .ace_foreign_line {
   position: absolute;
   z-index: -1;
-  background-color: #d8dee9;
+  background-color: #eceff4;
 }
 
 .ace_marker-layer .ace_active_debug_line {
 .ace_bracket {
   margin: 0 !important;
   border: 0 !important;
-  background-color: black;
+  background-color: #cccccc;
 }
 
 .ace_console_error {
 
 /* toolbar and selected tab */
 .rstudio-themes-flat .rstudio-themes-default .rstheme_center, .rstudio-themes-flat .rstudio-themes-default .gwt-TabLayoutPanelTabs .gwt-TabLayoutPanelTab-selected table.rstheme_tabLayoutCenter {
-  background: #e5e9f0 !important;
+  background: #eceff4 !important;
 }
 
 .rstudio-themes-flat .rstudio-themes-default .gwt-TabLayoutPanelTab-selected .gwt-Label {
 }
 
 .rstudio-themes-flat .rstheme_toolbarWrapper {
-  background: #e5e9f0 !important;
+  background: #eceff4 !important;
 }
 
 .rstudio-themes-flat .rstheme_toolbarWrapper button, .rstudio-themes-flat .rstheme_toolbarWrapper a, .rstudio-themes-flat .rstheme_toolbarWrapper div {
 }
 
 .rstudio-themes-flat .search, .rstudio-themes-flat.rstudio-themes-default-menus .search {
-  background: #e5e9f0 !important;
+  background: #eceff4 !important;
 }
 
 /* pane toolbars */
 .rstheme_secondaryToolbar, .rstudio-themes-flat .dataGridHeader {
-  background: #e5e9f0 !important;
+  background: #eceff4 !important;
 }
 
 /* menu background */
 }
 
 .rstudio-themes-flat .themedPopupPanel {
-  border: solid 1px black;
+  border: solid 1px #cccccc;
 }
 
 .rstudio-themes-flat .themedPopupPanel ~ div.popupContent div:nth-child(1) {
-  border: solid 1px black;
+  border: solid 1px #cccccc;
 }
 
 .rstudio-themes-flat .popupContent {
 
 .rstudio-themes-flat .popupContent:not(.popupMiddleCenterInner) div div:nth-child(2) {
   background: white !important;
-  border: solid 1px black;
+  border: solid 1px #cccccc;
 }
 
 .rstudio-themes-flat .gwt-PopupPanel .popupContent {
 .rstudio-themes-flat .rstudio-themes-default.rstudio-themes-scrollbars ::-webkit-scrollbar-thumb,
 .rstudio-themes-flat .rstudio-themes-default.rstudio-themes-scrollbars::-webkit-scrollbar-thumb,
 .rstudio-themes-flat.rstudio-themes-default-menus .rstudio-themes-scrollbars ::-webkit-scrollbar-thumb {
-  background: #d8dee9;
+  background: #eceff4;
   border: 4px solid white;
 }