tweak color themes and add $ui-line-active-selection

nord-polar-night-aurora.scss

 $ui-background           : $nord0;
 // $ui-background           : #262a33;
 $ui-foreground           : $nord4;
-$ui-code-chunk-background: $nord0;
+$ui-code-chunk-background: $nord1;
 $ui-selection            : transparentize($nord3, 0.6);
 $ui-cursor               : $nord9;
 $ui-margin-line          : lighten($ui-selection, 5%);
 // less common UI colors
 $ui-line-active           : transparentize($nord2, 0.6);
 $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-invisible             : $nord3;

oceanic-plus.scss

 // primary UI colors
 $ui-background           : $base00;
 $ui-foreground           : $base07;
-$ui-code-chunk-background: $base02;
+$ui-code-chunk-background: $base01;
 $ui-selection            : transparentize($base05, 0.6);
 $ui-cursor               : $base0A;
-$ui-margin-line          : lighten($ui-selection, 30%);
+$ui-margin-line          : transparentize($ui-selection, 0.25);
 $ui-gutter-color         : transparentize($ui-foreground, 0.5);
 $ui-gutter-background    : $ui-background;
 
 // less common UI colors
-$ui-line-active           : darken($ui-background, 2%);
-$ui-line-active-gutter    : $base02;
-$ui-line-find             : $base03;
-$ui-bracket               : $base03;
+$ui-line-active           : transparentize(darken($ui-background, 5%), 0.5);
+$ui-line-active-gutter    : $base01;
+$ui-line-active-selection : $base02;
+$ui-line-find             : $base01;
+$ui-bracket               : $base02;
 $ui-invisible             : $base03;
-$ui-indent-guide          : $ui-invisible;
+$ui-indent-guide          : $base02;
 $ui-debug-background      : lighten($ui-background, 10%);
 $ui-fold-arrows-background: $base08;
 $ui-fold-arrows-color     : $ui-foreground;
 $ui-rstudio-background         : $base01;
 $ui-rstudio-color              : $ui-foreground;
 $ui-rstudio-tabs-inactive      : $base01;
-$ui-rstudio-tabs-inactive-color: $base05;
+$ui-rstudio-tabs-inactive-color: $base04;
 $ui-rstudio-tabs-selected      : $base02;
-$ui-rstudio-tabs-selected-color: $base06;
+$ui-rstudio-tabs-selected-color: $base07;
 $ui-rstudio-toolbar            : $ui-rstudio-tabs-selected;
 $ui-rstudio-search             : $ui-rstudio-toolbar;
 $ui-completions-background     : $ui-background;

rsthemes/nord-polar-night-aurora.rstheme

 .ace_marker-layer .ace_foreign_line {
   position: absolute;
   z-index: -1;
-  background-color: #2e3440;
+  background-color: #3b4252;
 }
 
 .ace_marker-layer .ace_active_debug_line {
 }
 
 .ace_active-line ~ .ace_selection.ace_start {
-  background-color: #434c5e;
+  background-color: #4c566a;
 }
 
 .ace_keyword {

rsthemes/oceanic-plus.rstheme

 
 .ace_print-margin {
   width: 2px;
-  background: rgba(255, 255, 255, 0.4);
+  background: rgba(192, 197, 206, 0.15);
 }
 
 .ace_editor {
 
 .ace_marker-layer .ace_bracket {
   margin: -1px 0 0 -1px;
-  border: 1px solid #65737E;
+  border: 1px solid #4F5B66;
 }
 
 .ace_marker-layer .ace_active-line {
-  background: #18252d;
+  background: rgba(18, 29, 35, 0.5);
 }
 
 .ace_marker-layer .ace_selected-word {
 .ace_marker-layer .ace_foreign_line {
   position: absolute;
   z-index: -1;
-  background-color: #4F5B66;
+  background-color: #343D46;
 }
 
 .ace_marker-layer .ace_active_debug_line {
 .ace_marker-layer .ace_find_line {
   position: absolute;
   z-index: -1;
-  background-color: #65737E;
+  background-color: #343D46;
 }
 
 .ace_gutter-active-line {
-  background-color: #4F5B66;
+  background-color: #343D46;
 }
 
 .ace_fold {
 }
 
 .ace_indent-guide {
-  border-right: 1px solid #65737E;
+  border-right: 1px solid #4F5B66;
 }
 
 .ace_active-line ~ .ace_selection.ace_start {
-  background-color: #18252d;
+  background-color: #4F5B66;
 }
 
 .ace_keyword {
 .ace_bracket {
   margin: 0 !important;
   border: 0 !important;
-  background-color: #65737E;
+  background-color: #4F5B66;
 }
 
 .ace_console_error {
-  background-color: #65737E;
+  background-color: #343D46;
 }
 
 .ace_layer {
 }
 
 table.rstheme_tabLayoutCenter .gwt-Label, .rstudio-themes-flat .rstudio-themes-dark-grey .gwt-TabLayoutPanelTabs .gwt-Label, .rstheme_multiPodUtilityTabArea .gwt-Label {
-  color: #C0C5CE;
+  color: #A7ADBA;
 }
 
 /* toolbar and selected tab */
 }
 
 .rstudio-themes-flat .rstudio-themes-dark-grey .gwt-TabLayoutPanelTab-selected .gwt-Label {
-  color: #CDD3DE;
+  color: #D8DEE9;
 }
 
 .rstheme_toolbarWrapper {
 }
 
 .themedPopupPanel {
-  border: solid 1px #65737E;
+  border: solid 1px #4F5B66;
 }
 
 .themedPopupPanel ~ div.popupContent div:nth-child(1) {
-  border: solid 1px #65737E;
+  border: solid 1px #4F5B66;
 }
 
 .popupContent {
 
 .popupContent:not(.popupMiddleCenterInner) div div:nth-child(2) {
   background: #1B2B34 !important;
-  border: solid 1px #65737E;
+  border: solid 1px #4F5B66;
 }
 
 .terminal {

rstudio/_rstudio-dark.scss

 	border-right: 1px solid $ui-indent_guide;
 }
 .ace_active-line ~ .ace_selection.ace_start {
-	background-color: opacify($ui-line-active, 1);
+	background-color: $ui-line-active-selection;
 }
 .ace_keyword {
 	font-style: italic;