Style blank tab and keep private mode colors

Author: the-r3dacted

browser/base/content/blanktab.css

@@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+body {
+  background-color: light-dark(rgb(229, 227, 234), rgb(11, 10, 13)) !important;
+}

browser/base/content/blanktab.html

@@ -11,5 +11,6 @@
       http-equiv="Content-Security-Policy"
       content="default-src 'none'; style-src chrome:; object-src 'none'"
     />
+    <link rel="stylesheet" href="chrome://browser/content/blanktab.css" />
   </head>
 </html>

browser/base/jar.mn

@@ -33,6 +33,7 @@ browser.jar:
         content/browser/aboutTabCrashed.js            (content/aboutTabCrashed.js)
         content/browser/aboutTabCrashed.xhtml         (content/aboutTabCrashed.xhtml)
         content/browser/blanktab.html                 (content/blanktab.html)
+        content/browser/blanktab.css                  (content/blanktab.css)
         content/browser/browser.js                    (content/browser.js)
 *       content/browser/browser.xhtml                 (content/browser.xhtml)
         content/browser/browser-a11yUtils.js          (content/browser-a11yUtils.js)