code: function ieOpacityHack(decl, i) {
    //四舍五入
    var amount = Math.round(decl.value * 100)
    if (decl.prop == 'opacity') {
      var reBefore = decl.raws.before.replace(reBLANK_LINE, '$1')
  
      insertDecl(decl, i, {
        raws: {
          before: reBefore
        },
        prop: 'filter',
        value: 'alpha(opacity=' + amount + ')'
      })
    }
  }
docs: IE opacity hack
  转换为 IE filter