update elements and fix some bugs

lib/paper_item.dart

Index: lib/paper_item.dart
diff --git a/lib/paper_item.dart b/lib/paper_item.dart
index 03787f85ad5a776cdcca4f667b4c8ebe2f522d8e..b8dd018d20173606923353a955ed4729f05053d5 100644
--- a/lib/paper_item.dart
+++ b/lib/paper_item.dart
@@ -14,6 +14,8 @@ import 'iron_a11y_keys_behavior.dart';
 import 'paper_styles.dart';
 import 'paper_item_shared_styles.dart';
 
+/// 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>
@@ -33,10 +35,17 @@ import 'paper_item_shared_styles.dart';
 ///
 /// 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
 ///