setTimeout(function() { 

//更换下拉框箭头的背景，margin-top指距离顶部位置；background-size为图片尺寸；objectFit为自适应；backgroundRepeat为重复属性 

$('.bi-basic-button.cursor-pointer.bi-icon-button.horizon-center.bi-trigger-icon-button.overflow-hidden.pull-down-font.trigger-icon-button').css({

'height': '10px',

'margin-top': '10px',

'background-image': "url('/webroot/help/picture/xial.png ')",

'background-size': '12px 12px',

'objectFit': "cover",

'backgroundRepeat':"no-repeat",

});

}, 200) 

更多属性修改参考文档：【表单JS】JS修改新自适应表单控件属性-我的帆软

https://bbs.fanruan.com/thread-146510-1-1.html