fix: Fix unreadable text in high-contrast-mode (#35032)

app/javascript/styles/contrast/diff.scss

@@ -37,10 +37,6 @@
   color: $highlight-text-color;
 }
 
-.nothing-here {
-  color: $darker-text-color;
-}
-
 .report-dialog-modal__textarea::placeholder {
   color: $inverted-text-color;
 }

app/javascript/styles/contrast/variables.scss

@@ -21,5 +21,5 @@ $ui-highlight-color: $classic-highlight-color !default;
   $action-button-color: lighten($ui-base-color, 50%),
   $inverted-text-color: $black,
   $lighter-text-color: darken($ui-base-color, 6%),
-  $light-text-color: darken($ui-primary-color, 40%)
+  $light-text-color: $classic-primary-color
 );