Import Polymer 0.8 and several key elements.

third_party/polymer/v0_8/components/paper-checkbox/paper-checkbox.css

+/*
+Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+*/
+
+:host {
+  display: inline-block;
+  white-space: nowrap;
+}
+
+.hidden {
+  display: none;
+}
+
+#checkboxContainer {
+  display: inline-block;
+  position: relative;
+  width: 18px;
+  height: 18px;
+  cursor: pointer;
+  -webkit-transform: translateZ(0);
+  transform: translateZ(0);
+  vertical-align: middle;
+}
+
+:host #ink {
+  position: absolute;
+  top: -15px;
+  left: -15px;
+  width: 48px;
+  height: 48px;
+  color: var(--paper-checkbox-unchecked-ink-color);
+}
+
+:host #ink[checked] {
+  color: var(--paper-checkbox-checked-ink-color);
+}
+
+:host #checkbox {
+  position: relative;
+  box-sizing: border-box;
+  height: 100%;
+  border: solid 2px;
+  border-color: var(--paper-checkbox-unchecked-color);
+  border-radius: 2px;
+  pointer-events: none;
+  -webkit-transition: background-color 140ms, border-color 140ms;
+  transition: background-color 140ms, border-color 140ms;
+}
+
+/* checkbox checked animations */
+#checkbox.checked #checkmark {
+  -webkit-animation: checkmark-expand 140ms ease-out forwards;
+  animation: checkmark-expand 140ms ease-out forwards;
+}
+
+@-webkit-keyframes checkmark-expand {
+  0% {
+    top: 9px;
+    left: 6px;
+    width: 0px;
+    height: 0px;
+  }
+  100% {
+    top: -1px;
+    left: 4px;
+    width: 5px;
+    height: 10px;
+  }
+}
+
+@keyframes checkmark-expand {
+  0% {
+    top: 9px;
+    left: 6px;
+    width: 0px;
+    height: 0px;
+  }
+  100% {
+    top: -1px;
+    left: 4px;
+    width: 5px;
+    height: 10px;
+  }
+}
+
+:host #checkbox.checked {
+  background-color: var(--paper-checkbox-checked-color);
+  border-color: var(--paper-checkbox-checked-color);
+}
+
+:host #checkmark {
+  -webkit-transform: rotate(45deg);
+  transform: rotate(45deg);
+  position: absolute;
+  top: -1px;
+  left: 4px;
+  width: 5px;
+  height: 10px;
+  border-style: solid;
+  border-top: none;
+  border-left: none;
+  border-right-width: 2px;
+  border-bottom-width: 2px;
+  border-color: white;
+}
+
+/* label */
+#checkboxLabel {
+  position: relative;
+  display: inline-block;
+  vertical-align: middle;
+  padding-left: 8px;
+  white-space: normal;
+  pointer-events: none;
+}
+
+#checkboxLabel[hidden] {
+  display: none;
+}
+
+/* disabled state */
+:host([disabled]) {
+  pointer-events: none;
+}
+
+:host([disabled]) #checkbox {
+  opacity: 0.33;
+  border-color: var(--paper-checkbox-unchecked-color);
+}
+
+:host([disabled][checked]) #checkbox {
+  background-color: var(--paper-checkbox-unchecked-color);
+}