HarmonyOS 自定义Toast显示，多了一个白色背景

使用promptAction.openCustomDialog自定义Toast，显示时多了一块白色背景，但是代码没有相关设置；请问如何去除白色背景？

示例代码：

import promptAction from '@ohos.promptAction'  
let customDialogId: number = 0  
@Builder  
function customDialogBuilder(text: string) {  
  Column() {  
    Text (text)  
      .fontSize (18)  
      .fontColor(Color.White)  
      .textAlign(TextAlign.Center)  
      .backgroundColor(Color.Transparent)  
      .maxLines(-1)  
      .constraintSize ({ maxWidth: '70%' })  
  }  
  .backgroundColor(Color.Red)  
  .justifyContent(FlexAlign.Center)  
  .padding({ top: 16, left: 20, bottom: 16, right: 20 })  
  .borderRadius(12)  
}  
@Entry  
@Component  
struct showTextToast {  
  build() {  
  }  
  showAlignmentToast(text : string, alignment:DialogAlignment) {  
    promptAction.openCustomDialog({  
      builder: customDialogBuilder.bind(this,text),  
      alignment: alignment,  
      maskColor: Color.Green,  
      backgroundColor: Color.Red,  
      width:'10%',  
      cornerRadius: 0  
    }).then((dialogId: number) => {  
      customDialogId = dialogId  
      this.autoClose(dialogId)  
    })  
  }  
  autoClose(dialogId: number){  
    let timeId = setTimeout(() => {  
      promptAction.closeCustomDialog(dialogId)  
      clearTimeout(timeId)  
    },1500);  
  }  
}@Entry  
@Component  
struct showTextToast {  
  build() {  
  }  
  showAlignmentToast(text : string, alignment:DialogAlignment) {  
    promptAction.openCustomDialog({  
      builder: customDialogBuilder.bind(this,text),  
      alignment: alignment,  
      maskColor: Color.Green,  
      backgroundColor: Color.Red,  
      cornerRadius: 0  
    }).then((dialogId: number) => {  
      customDialogId = dialogId  
      this.autoClose(dialogId)  
    })  
  }  
  autoClose(dialogId: number){  
    let timeId = setTimeout(() => {  
      promptAction.closeCustomDialog(dialogId)  
      clearTimeout(timeId)  
    },1500);  
  }  
}1.
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