New way to load slack dark theme

Windows 10 Dark Theme/Slack/install.md

@@ -14,15 +14,41 @@ So, in order to do this now before Slack officially supports it, do the followin
  - Add the following to the end of the **ssb-interop.js** file
 
 ```
-document.addEventListener('DOMContentLoaded', function() {
-  $.ajax({
+document.addEventListener("DOMContentLoaded", function() {
 
-    url: 'https://raw.githubusercontent.com/angelsix/youtube/develop/Windows%2010%20Dark%20Theme/Slack/slack-dark.css',
-    success: function(css) {
-      $("<style></style>").appendTo('head').html(css);
-    }
+   // Then get its webviews
+   let webviews = document.querySelectorAll(".TeamView webview");
+
+   // Fetch our CSS in parallel ahead of time
+   const cssPath = 'https://raw.githubusercontent.com/angelsix/youtube/develop/Windows%2010%20Dark%20Theme/Slack/slack-dark.css';
+   let cssPromise = fetch(cssPath).then(response => response.text());
+
+   // Insert a style tag into the wrapper view
+   cssPromise.then(css => {
+      let s = document.createElement('style');
+      s.type = 'text/css';
+      s.innerHTML = css;
+      document.head.appendChild(s);
+   });
+
+   // Wait for each webview to load
+   webviews.forEach(webview => {
+      webview.addEventListener('ipc-message', message => {
+         if (message.channel == 'didFinishLoading')
+            // Finally add the CSS into the webview
+            cssPromise.then(css => {
+               let script = `
+                     let s = document.createElement('style');
+                     s.type = 'text/css';
+                     s.id = 'slack-custom-css';
+                     s.innerHTML = \`${css}\`;
+                     document.head.appendChild(s);
+                     `
+               webview.executeJavaScript(script);
+            })
       });
    });
+});
 ```
 
  - Now close Slack (including in the Taskbar)