Fixed #25967 -- Indicated required fields in admin.TabularInline headers.

django/contrib/admin/static/admin/css/base.css

@@ -272,6 +272,10 @@ tfoot td {
     border-top: 1px solid #eee;
 }
 
+thead th.required {
+    color: #000;
+}
+
 tr.alt {
     background: #f6f6f6;
 }