quick-alert.html

<link rel="import" href="bower_components/polymer/polymer.html">

<dom-module id="quick-alert">
  <style>
    :host {
      display: block;
      position: fixed;
      top: 0;
      left: 0;
      right: 0;
    }
    .alert {
      background-color: #4CAF50;
      color: white;
      padding: 16px;
      font-family: Roboto, Helvetica, sans-serif;
    }
    .close {
      float: right;
    }
  </style>
  <template>
    <div class="alert">
      <content></content><span class="close">{{closeBtn}}</span>
    </div>
  </template>
</dom-module>

<script>
  'use strict';

  class QuickAlert {
    static configureClass(clazz) {
      clazz.is = 'quick-alert';
      clazz.properties = {
        closeBtn: {
          type: String,
          value: 'x'
        }
      };
      super.configureClass(clazz);
    }
  }

  Polymer(QuickAlert);
</script>