Make mobile top navigation bar have the same background color as the side navigation header. (#1132)

Author: eerimoq

sphinx_rtd_theme/layout.html

@@ -174,7 +174,7 @@
     <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">
 
       {#- MOBILE NAV, TRIGGLES SIDE NAV ON TOGGLE #}
-      <nav class="wy-nav-top" aria-label="{{ _('Top') }}">
+      <nav class="wy-nav-top" aria-label="{{ _('Top') }}" {% if theme_style_nav_header_background %} style="background: {{theme_style_nav_header_background}}" {% endif %}>
         {%- block mobile_nav %}
           <i data-toggle="wy-nav-top" class="fa fa-bars"></i>
           <a href="{{ pathto(master_doc) }}">{{ project }}</a>