<view class="stepper">
  <view class="reduce btn" bindtap="reduce">
    <view class="line {{number === min ? 'gray' : ''}}"></view>
  </view>
  <input class="number" type="number" value="{{number}}" bindinput="change"/>
  <view class="add btn" bindtap="add">
    <view class="start-cell {{number === max ? 'gray' : ''}}">
      <view class="left-line"></view>
      <view class="right-line"></view>
    </view>
  </view>
</view>