view: use aboutReaderContent.css from Firefox's reading mode

see issue #77

data/aboutReaderContent.css

@@ -0,0 +1,113 @@
+/* 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/. */
+
+#moz-reader-content {
+  display: none;
+  font-size: 1em;
+  line-height: 1.6em;
+}
+
+h1,
+h2,
+h3 {
+  font-weight: bold;
+}
+
+h1 {
+  font-size: 1.6em;
+  line-height: 1.25em;
+}
+
+h2 {
+  font-size: 1.2em;
+  line-height: 1.51em;
+}
+
+h3 {
+  font-size: 1em;
+  line-height: 1.66em;
+}
+
+a {
+  text-decoration: underline;
+  font-weight: normal;
+}
+
+a,
+a:visited,
+a:hover,
+a:active {
+  color: #0095dd;
+}
+
+* {
+  max-width: 100%;
+  height: auto;
+}
+
+p,
+code,
+pre,
+blockquote,
+ul,
+ol,
+li,
+figure,
+.wp-caption {
+  margin: 0 0 30px 0;
+}
+
+p > img:only-child,
+p > a:only-child > img:only-child,
+.wp-caption img,
+figure img {
+  display: block;
+}
+
+img[moz-reader-center] {
+  margin-left: auto;
+  margin-right: auto;
+}
+
+.caption,
+.wp-caption-text,
+figcaption {
+  font-size: 0.9em;
+  line-height: 1.48em;
+  font-style: italic;
+}
+
+code,
+pre {
+  white-space: pre-wrap;
+}
+
+blockquote {
+  padding: 0;
+  -moz-padding-start: 16px;
+}
+
+ul,
+ol {
+  padding: 0;
+}
+
+ul {
+  -moz-padding-start: 30px;
+  list-style: disc;
+}
+
+ol {
+  -moz-padding-start: 30px;
+  list-style: decimal;
+}
+
+/* Hide elements with common "hidden" class names */
+.visually-hidden,
+.visuallyhidden,
+.hidden,
+.invisible,
+.sr-only {
+  display: none;
+}

data/gnome-news.gresource.xml

@@ -7,5 +7,6 @@
     <file compressed="true" preprocess="xml-stripblanks">Menu.ui</file>
     <file compressed="true" preprocess="xml-stripblanks">HeaderBar.ui</file>
     <file compressed="true">application.css</file>
+    <file compressed="true">aboutReaderContent.css</file>
   </gresource>
 </gresources>

gnomenews/view.py

@@ -173,10 +173,14 @@ class FeedView(Gtk.Stack):
     def __init__(self, tracker, post):
         Gtk.Stack.__init__(self,
                            transition_type=Gtk.StackTransitionType.CROSSFADE)
+        stylesheet = Gio.File.new_for_uri('resource:///org/gnome/News/aboutReaderContent.css')
         webview = WebKit2.WebView()
         if post.content:
             html = """
             <style>
+            """
+            html += stylesheet.load_contents(None)[1].decode()
+            html += """
               * {
                 max-width: 100%%;
                 height: auto;