Hide specific category on site

Hi,

How can I hide a specific LMS category (ID 21) in the main dropdown menu using CSS (display:none). I still need the category to be shown in the Archiver.

<div class="stm_lms_categories_dropdown">
	<div class="stm_lms_categories_dropdown__parents"> (Category ID 21)
		<div class="stm_lms_categories_dropdown__parent ">
			<a href="https://localdomain.co/explore/body/" class="sbc_h">
			<span class="stm_lms_cat_toggle"></span><div class="stm_lms_categories_dropdown__childs">
		</div>
		<div class="stm_lms_categories_dropdown__parent ">
		<div class="stm_lms_categories_dropdown__parent ">
		<div class="stm_lms_categories_dropdown__parent ">
		<div class="stm_lms_categories_dropdown__parent ">
	</div>
</div>

Regards

Max