moving width to css

assets/css/src/admin.styl

@@ -29,3 +29,5 @@
 @require 'mp2migrator'
 
 @require '../../../node_modules/react-confirm-alert/src/react-confirm-alert.css'
+
+@require 'newsletter_templates'

assets/css/src/newsletter_templates.styl

@@ -0,0 +1,7 @@
+@require 'newsletter_editor/variables'
+
+.mailpoet_template_iframe
+  position: absolute
+  z-index: -9999
+  width: $newsletter-width
+  max-width: $newsletter-width

assets/js/src/newsletters/send.jsx

@@ -92,10 +92,8 @@ define(
       },
       saveTemplate: function (response, done) {
         const iframe = document.createElement('iframe');
-        iframe.width = 660;
         iframe.src = response.meta.preview_url;
         iframe.onload = () => {
-          setTimeout(() => {
           html2canvas(iframe.contentDocument.documentElement).then((thumbnail) => {
             document.body.removeChild(iframe);
             MailPoet.Ajax.post({
@@ -112,10 +110,9 @@ define(
               },
             }).then(done).fail(this.showError);
           });
-          }, 500);
         };
         // just to hide the iframe
-        iframe.style.cssText ='position: absolute; opacity:0; z-index: -9999';
+        iframe.className ='mailpoet_template_iframe';
         document.body.appendChild(iframe);
       },
       handleSend: function (e) {