diff --git a/static/css/s2.css b/static/css/s2.css
index a10920c449..128071435d 100644
--- a/static/css/s2.css
+++ b/static/css/s2.css
@@ -606,7 +606,7 @@ input.noselect {
   font-size: 18px;
 }
 .mobileNavMenu {
-  position: absolute;
+  position: fixed;
   height: calc(100vh - 60px);
   box-sizing: border-box;
   top: 60px;
@@ -621,6 +621,12 @@ div:has(#bannerMessage) + .readerApp.singlePanel .mobileNavMenu {
   height: calc(100vh - 180px);
   top: 180px;
 }
+@supports not selector(:has(a, b)) {
+  /* Fallback for when :has() is unsupported */
+  .mobileNavMenu {
+    position: absolute;
+  }
+}
 
 .mobileNavMenu.closed {
   display: none;