Changing style for class inside shadow root

I want to adjust the style for an element inside shadow root. The problem is, that I need to target the class.

HTML inside DOM

<menu-flyout-item>
 #shadow-root
  <div class="menu-flyout-item" part="base">...</div>
</menu-flyout-item>

Style for the class menu-flyout-item inside HTML DOM

.menu-flyout-item {
 padding: 0 10px;
}

Targeting scale-menu-flyout-item > div::part(base) as well as scale-menu-flyout-item > .menu-flyout-item won´t change the padding. Do you have any advice how to target the class inside shadow div element?