ction() {
          if (this.up) {
            if (this.z < 5) {
              this.z += 1;
            } else {
              this.z -= 1;
              this.up = false;
            }
          } else {
            if (this.z > 0) {
              this.z -= 1;
            } else {
              this.z += 1;
              this.up = true;
            }
          }
        }
      });
    </script>
  </polymer-element>

  <section>
    <div>
      <x-shadow id="card" z="0" class="card"></x-shadow>
    </div>
 