Fix sidebar focus toggle

This diverges from upstream, but it fixes a visual regression that I
find too insidious to merge. When you close the sidebar, the toggle
remains colored, and you have to click elsewhere to take away focus and
un-color it. For more details, see #12. Thanks to @ryan-robeson who
investigated the issue.

static/css/lanyon.css

@@ -234,14 +234,12 @@ a.sidebar-nav-item:focus {
 }
 
 .sidebar-toggle:active,
-#sidebar-checkbox:focus ~ .sidebar-toggle,
 #sidebar-checkbox:checked ~ .sidebar-toggle {
   color: #fff;
   background-color: #555;
 }
 
 .sidebar-toggle:active:before,
-#sidebar-checkbox:focus ~ .sidebar-toggle:before,
 #sidebar-checkbox:checked ~ .sidebar-toggle:before {
   background-image: -webkit-linear-gradient(to bottom, #fff, #fff 20%, #555 20%, #555 40%, #fff 40%, #fff 60%, #555 60%, #555 80%, #fff 80%, #fff 100%);
   background-image:    -moz-linear-gradient(to bottom, #fff, #fff 20%, #555 20%, #555 40%, #fff 40%, #fff 60%, #555 60%, #555 80%, #fff 80%, #fff 100%);