how do i add dropdown arrow to folders in the navigator on squarespace header

How do I add a drop down arrow to my about and our approach navigator. My website link is https://www.flowersequitypartners.com/ and my website image is attached below.

my reference site is https://www.vestarcapital.com/ and the image of the reference site and the kind of arrow i want is just like the one on the reference site's 

Add this code to Website Tools (under Not Linked) > Custom CSS

/* dropdown arrow */
a.header-nav-folder-title:after {
    content: "\e009";
    font-family: 'squarespace-ui-font';
    position: relative;
    top: 2px;
}