Change appearance of selectpicker filter dropdown Bootstrap/JS/ CSS

I have attached two pictures. and a PHP file that contains the full content. I have a selectpicker filter dropdown picture (A) that I was to change the appearce to look the the field below it picture.(B) ( ignore the icon). At the moment as you can see the selectpicker filter is white and looks like a dropdown.


So when the page loads it looks like field B. when the user clicks in to the field it will open the drop down. So field( B) will be a button.