按下back时关闭弹出的浮层

"back": {
"before": [
{
"popupSelector":".dialogbox",
"closeSelector": ".tip_btn.bg_f.f_b",
"eventType": "click"
}
]
}
以上是代码，下图是h5代码，如何才能正确设置按下back时关闭弹出的浮层