fix highlight of text selected for light mode

stylesheets/_session.scss

@@ -38,7 +38,9 @@ textarea {
     user-select: text;
 
     &::selection {
-      background: rgba($session-color-green, 0.6);
+      @include themify($themes) {
+        background: themed('textHighlight');
+      }
     }
   }
 }

stylesheets/themes.scss

@@ -25,6 +25,7 @@ $themes: (
       textColor: $black,
     textColorSubtle: #a0a0a0,
     textColorOpposite: $white,
+    textHighlight: rgba($black, 0.2),
     // inbox
       inboxBackground: $white,
     // buttons
@@ -74,6 +75,7 @@ $themes: (
       textColor: $white,
     textColorSubtle: #a0a0a0,
     textColorOpposite: $black,
+    textHighlight: rgba($accentDarkTheme, 0.6),
     // inbox
       inboxBackground: linear-gradient(180deg, #171717 0%, #121212 100%),
     // buttons