Keep issue dialog above site navigation

frontend/app/ops-redesign.css

@@ -2654,6 +2654,10 @@ button:disabled,
   overflow: hidden;
 }
 
+.issue-reports-column.has-open-modal {
+  z-index: 2000;
+}
+
 .issue-reports-column > .issue-history-heading {
   align-items: center;
   padding: 14px 15px;

frontend/app/portal/PortalClient.tsx

@@ -2020,7 +2020,9 @@ export default function PortalClient({ workspace }: PortalClientProps) {
         </>
       ) : null}
 
-      <div className={workspace === 'issue' ? 'issue-reports-column' : 'portal-lower-content'}>
+      <div className={workspace === 'issue'
+        ? `issue-reports-column ${selectedItemId != null ? 'has-open-modal' : ''}`
+        : 'portal-lower-content'}>
       {workspace === 'issue' ? (
         <div className="issue-history-heading">
           <div>