Fix MR SAST reports in dark mode

app/assets/stylesheets/page_bundles/reports.scss

@@ -8,14 +8,14 @@
 
   .report-block-list-issue-parent {
     padding: $gl-padding-top $gl-padding;
-    border-top: 1px solid $border-color;
+    border-top: 1px solid var(--border-color, $border-color);
   }
 }
 
 .report-block-container {
-  border-top: 1px solid $border-color;
+  border-top: 1px solid var(--border-color, $border-color);
   padding: $gl-padding - 2;
-  background-color: $gray-light;
+  background-color: var(--gray-50, $gray-10);
 
   // Clean MR widget CSS
   line-height: 20px;

changelogs/unreleased/281020-dark-mode-isn-t-compabile-with-secure-mr-widget.yml

+---
+title: Fix secure MR widget colors in dark mode
+merge_request: 47352
+author:
+type: fixed