toggle only available when :target is supported

docs/source/javascripts/modernizr.selectors.js

@@ -0,0 +1,55 @@
+// selectorSupported lovingly lifted from the mad italian genius, diego perini
+// http://javascript.nwbox.com/CSSSupport/
+function selectorSupported(selector){
+
+  var support, link, sheet, doc = document,
+      root = doc.documentElement,
+      head = root.getElementsByTagName('head')[0],
+
+      impl = doc.implementation || {
+              hasFeature: function() {
+                  return false;
+              }
+      },
+
+  link = doc.createElement("style");
+  link.type = 'text/css';
+
+  (head || root).insertBefore(link, (head || root).firstChild);
+
+  sheet = link.sheet || link.styleSheet;
+
+  if (!(sheet && selector)) return false;
+
+  support = impl.hasFeature('CSS2', '') ?
+
+              function(selector) {
+                  try {
+                      sheet.insertRule(selector + '{ }', 0);
+                      sheet.deleteRule(sheet.cssRules.length - 1);
+                  } catch (e) {
+                      return false;
+                  }
+                  return true;
+
+              } : function(selector) {
+
+                  sheet.cssText = selector + ' { }';
+                  return sheet.cssText.length !== 0 && !(/unknown/i).test(sheet.cssText) && sheet.cssText.indexOf(selector) === 0;
+              };
+
+  return support(selector);
+
+};
+
+Modernizr.addTest('target',function(){
+  return selectorSupported(':target');
+}).addTest('not',function(){
+  return selectorSupported(':not(p)');
+}).addTest('last-child',function(){
+  return selectorSupported(':last-child');
+}).addTest('nth-child',function(){
+  return selectorSupported(':nth-child(2)');
+}).addTest('nth-of-type',function(){
+  return selectorSupported(':nth-of-type(2)');
+})

docs/source/partials/_head.haml

@@ -8,4 +8,5 @@
   %meta{:content => "width=device-width", :name => "viewport"}
 
   = stylesheet_link_tag "site.css"
-  = javascript_include_tag "modernizr-2.5.3.min.js"
+  = javascript_include_tag "modernizr-2.5.3.min.js"
+  = javascript_include_tag "modernizr.selectors.js"

docs/source/stylesheets/_modules/_toggle.scss

@@ -2,10 +2,11 @@
 // Grid Toggle
 
 .grid-toggle {
-  // display: none;
+  display: none;
   position: absolute;
   top: .5em;
   right: .5em;
+  .target & { display: block; }
 }
 
 .on, .off {