Meta theme color (#547)

* feat(theme/index): Add meta tag for theme-color

* feat(theme/book): Sync theme-color meta tag with the current theme

src/theme/book.js

@@ -161,6 +161,10 @@ $( document ).ready(function() {
             ace_theme = "ace/theme/dawn";
         }
 
+        setTimeout(function() {
+            document.querySelector('meta[name="theme-color"]').content = getComputedStyle(document.body).backgroundColor;
+        }, 1);
+
         if (window.ace && window.editors) {
             window.editors.forEach(function(editor) {
                 editor.setTheme(ace_theme);

src/theme/index.hbs

@@ -6,6 +6,7 @@
         <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
         <meta name="description" content="{{ description }}">
         <meta name="viewport" content="width=device-width, initial-scale=1">
+        <meta name="theme-color" content="#ffffff" />
 
         <base href="{{ path_to_root }}">