HarmonyOS 鸿蒙Next Shadow List里面给ListItem设置的shadow 为什么底部看不到

通过设置第一个item和最后一个item的offsetY来展示shadow，参考demo

@Entry
@Component
struct ListExample {
  private arr: number[] = [0, 1, 2, 3, 4, 5, 6,7,8]
  @State y: number = 0

  build() {
    Column() {
      List({ space: 20, initialIndex: 0 }) {
        ForEach(this.arr, (item: number) => {
          ListItem() {
            Text('' + item)
              .width('100%')
              .height(100)
              .fontSize(16)
              .textAlign(TextAlign.Center)
              .borderRadius(10)
              .backgroundColor(0xFFFFFF)
              .shadow({
                radius: 10,
                color: Color.Green,
                offsetX: 20,
                offsetY: 20
              })
            // .layoutWeight(1)
          }
          .offset({ y: this.y })

        }, (item: string) => item)
      }
      .listDirection(Axis.Vertical) // 排列方向
      .scrollBar(BarState.Off)
      .friction(0.6)
      .divider({
        strokeWidth: 2,
        color: 0xFFFFFF,
        startMargin: 20,
        endMargin: 20
      }) // 每行之间的分界线
      .edgeEffect(EdgeEffect.Spring) // 边缘效果设置为Spring
      .onScrollIndex((firstIndex: number, lastIndex: number, centerIndex: number) => {
        console.info('first' + firstIndex)
        console.info('last' + lastIndex)
        console.info('center' + centerIndex)
      })
      .onReachEnd(() => {
        this.y = -10
      })
      .onReachStart(() => {
        this.y = 0
      })
      .onScrollVisibleContentChange((start: VisibleListContentInfo, end: VisibleListContentInfo) => {
        console.log(' start index: ' + start.index +
          ' start item group area: ' + start.itemGroupArea +
          ' start index in group: ' + start.itemIndexInGroup)
        console.log(' end index: ' + end.index +
          ' end item group area: ' + end.itemGroupArea +
          ' end index in group: ' + end.itemIndexInGroup)
      })
      .onDidScroll((scrollOffset: number, scrollState: ScrollState) => {
        console.info(`onScroll scrollState = ScrollState` + scrollState + `, scrollOffset = ` + scrollOffset)
      })
      .width('90%')

      // .layoutWeight(1)
    }

    .width('100%')
    .height('100%')
    .backgroundColor(0xDCDCDC)
  }
}