adding anti-flicker for google

tool/template-base.html

@@ -33,6 +33,14 @@
     <meta name="msapplication-config" content="{{currentpage.prefix}}assets/favicons/browserconfig.xml">
     <meta name="theme-color" content="#25A768">
 
+    <!-- Google anti-flicker snippet -->
+    <style>.async-hide { opacity: 0 !important} </style>
+    <script>(function(a,s,y,n,c,h,i,d,e){s.className+=' '+y;h.start=1*new Date;
+    h.end=i=function(){s.className=s.className.replace(RegExp(' ?'+y),'')};
+    (a[n]=a[n]||[]).hide=h;setTimeout(function(){i();h.end=null},c);h.timeout=c;
+    })(window,document.documentElement,'async-hide','dataLayer',4000,
+    {'GTM-KCQZ3L8':true});</script>
+
     <!-- jQuery -->
     <script src="{{currentpage.prefix}}assets/vendor/jquery-3.6.0.min.js"></script>