refs #19224 [finc] set mainbody to full width for xs

themes/finc/scss/compiled.scss

@@ -1866,6 +1866,12 @@ footer {
   }
 }
 
+.mainbody {
+  @media screen and (max-width: $screen-xs-max) {
+    width: 100%;
+  }
+}
+
 footer {
   border-top: 0;
   padding-top: ($grid-gutter-width / 1.5);