Use page backdrop with the terminal

IPython/html/static/terminal/less/terminal.less

@@ -1,3 +1,15 b''
+body.terminal-app {
+  background: @page-backdrop-color;
+
+  #header {
+    background: @body-bg;
+    .box-shadow(@global-shadow);
+
+    .header-bar {
+      margin-bottom: -1px;
+    }
+  }
+
 .terminal {
   float: left;
   font-family: monospace;
@@ -21,3 +33,4 b''
 #terminado-container {
   margin-top: @page-header-padding;
 }
+}

IPython/html/templates/terminal.html

@@ -6,6 +6,7 b''
 
 data-base-url="{{base_url}}"
 data-ws-path="{{ws_path}}"
+class="terminal-app"
 
 {% endblock %}