fix(cc-dark-theme): minor improvements

- Fix dialog close button color.
- Fix color for error messages when loading threads.
- Fix "duplicate thread" dialog buttons color.

Fixed: twpowertools:193
Change-Id: Ie4048a0faf297b7cad9a75030bf9c63a42914b6d
diff --git a/src/ccDarkTheme/components/dialogs/_dialog.scss b/src/ccDarkTheme/components/dialogs/_dialog.scss
index 5ae0bf1..4f3570c 100644
--- a/src/ccDarkTheme/components/dialogs/_dialog.scss
+++ b/src/ccDarkTheme/components/dialogs/_dialog.scss
@@ -10,6 +10,10 @@
   color: var(--TWPT-primary-text-alt)!important;
 }
 
+material-dialog header material-button:is(.close-button, [debugid="close-button"]) material-icon {
+  color: var(--TWPT-subtle-button-background)!important;
+}
+
 ec-movable-dialog[showminimize] material-dialog .dialog-header .title, ec-movable-dialog[showminimize] material-dialog header material-icon {
   color: var(--TWPT-primary-background)!important;
 }