Update theme switcher styling

src/newsreader/scss/components/index.scss

@@ -3,6 +3,7 @@
 @import './main/index';
 @import './navbar/index';
 @import './loading-indicator/index';
+@import './theme-switcher/index';
 
 @import './modal/index';
 

src/newsreader/scss/components/navbar/_navbar.scss

@@ -1,6 +1,7 @@
 .nav {
   display: flex;
   justify-content: center;
+  align-items: center;
 
   margin: 0 0 5px 0;
   padding: 10px 0;

src/newsreader/scss/components/theme-switcher/_theme-switcher.scss

@@ -0,0 +1,5 @@
+.theme-switcher {
+  &:hover {
+    cursor: pointer;
+  }
+}

src/newsreader/scss/components/theme-switcher/index.scss

@@ -0,0 +1 @@
+@import './theme-switcher';

src/newsreader/templates/base.html

@@ -28,7 +28,7 @@
         {% endif %}
       </ol>
 
-      <button class="theme-switcher"></button>
+      <i class="theme-switcher gg-dark-mode"></i>
     </nav>
 
     {% if messages %}