Style the "+x" Icon, when using max-options-available and multiple on sl-select

[glennDittmann]

I have an <sl-select multiple max-options-visible="2"> and I want to style the +x icon that appears, when more than 2 items are selected, as I already styled all the other parts to my needs.
How can I access this element?

E.g. I want to remove the border.
This

.multiselect::part(tag__base) {
  border: none;
}

works for all the tags, but the +x.
Thanks for your help in advance.