Fix background color after it was removed in crrev.com/c/5449892

Bug: none
Change-Id: I646732954cc0c9bcb99c4bf35f79512ed40041e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5469081
Auto-Submit: Kristi Saney <kristislee@google.com>
Reviewed-by: Lauren Winston <lwinston@google.com>
Commit-Queue: Lauren Winston <lwinston@google.com>
Cr-Commit-Position: refs/heads/main@{#1290257}
diff --git a/chrome/browser/resources/side_panel/read_anything/app.html b/chrome/browser/resources/side_panel/read_anything/app.html
index fc71daa..6d610e4 100644
--- a/chrome/browser/resources/side_panel/read_anything/app.html
+++ b/chrome/browser/resources/side_panel/read_anything/app.html
@@ -22,6 +22,7 @@
   }
 
   #appFlexParent #container-parent {
+    background: var(--background-color);
     height: 100%;
     overflow: auto;
   }