update elements and fix some bugs

lib/src/paper-item/paper-item.html

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 <link rel="import" href="../polymer/polymer.html">
 <link rel="import" href="../iron-behaviors/iron-control-state.html">
 <link rel="import" href="../iron-behaviors/iron-button-state.html">
 <link rel="import" href="../paper-styles/paper-styles.html">
 <link rel="import" href="paper-item-shared-styles.html">
 
 <!--
+Material design: [Lists](https://www.google.com/design/spec/components/lists.html)
+
 `<paper-item>` is a non-interactive list item. By default, it is a horizontal flexbox.
 
     <paper-item>Item</paper-item>
 
 Use this element with `<paper-item-body>` to make Material Design styled two-line and three-line
 items.
 
     <paper-item>
       <paper-item-body two-line>
         <div>Show your status</div>
         <div secondary>Your status is visible to everyone</div>
       </paper-item-body>
       <iron-icon icon="warning"></iron-icon>
     </paper-item>
 
 ### Styling
 
 The following custom properties and mixins are available for styling:
 
-Custom property | Description | Default
-----------------|-------------|----------
-`--paper-item-min-height` | Minimum height of the item | `48px`
-`--paper-item`            | Mixin applied to the item  | `{}`
+Custom property               | Description                                    | Default
+------------------------------|------------------------------------------------|----------
+`--paper-item-min-height`     | Minimum height of the item                     | `48px`
+`--paper-item`                | Mixin applied to the item                      | `{}`
+`--paper-item-selected-weight`| The font weight of a selected item             | `bold`
+`--paper-item-selected`       | Mixin applied to selected paper-items                | `{}`
+`--paper-item-disabled-color` | The color for disabled paper-items             | `--disabled-text-color`
+`--paper-item-disabled`       | Mixin applied to disabled paper-items        | `{}`
+`--paper-item-focused`        | Mixin applied to focused paper-items         | `{}`
+`--paper-item-focused-before` | Mixin applied to :before focused paper-items | `{}`
+
 
 ### Accessibility
 
 This element has `role="listitem"` by default. Depending on usage, it may be more appropriate to set
 `role="menuitem"`, `role="menuitemcheckbox"` or `role="menuitemradio"`.
 
     <paper-item role="menuitemcheckbox">
       <paper-item-body>
         Show your status
       </paper-item-body>
@@ skipping 30 matching lines @@
         tabindex: '0'
       },
 
       behaviors: [
         Polymer.IronControlState,
         Polymer.IronButtonState
       ]
     });
   </script>
 </dom-module>