Dropdown arrow not showing on iDeal

Hi,

I’m beginning a online webshop.
Bought the theme ‘fixteam’ but there unwilling to help me.

Once a customer is ready to pay at checkout, there’s a iDeal option and there a multiple options within the dropdown. But before the page loads you can clearly see a arrow next to it. But it disappears once the page is loaded.

I already added this to the custom css :

select:not(.esg-sorting-select):not([class*="trx_addons_attrib_"]) {

	
  visibility: visible;
/*	width: 650px; */
background-color: white;
	height: auto;
	border: 2px solid #ddd;
	width: auto;
}

Is there something else im missing?

The page in question is : https://www.phonefixed.nl/afrekenen/

Thanks in advance