diff --git a/phpBB/adm/style/acp_posting_buttons.html b/phpBB/adm/style/acp_posting_buttons.html
index fd07f7499b..e5f96b0c22 100644
--- a/phpBB/adm/style/acp_posting_buttons.html
+++ b/phpBB/adm/style/acp_posting_buttons.html
@@ -8,8 +8,6 @@
 // ]]>
 </script>
 
-{% include 'mentions_templates.html' %}
-
 <!-- INCLUDEJS {T_ASSETS_PATH}/javascript/editor.js -->
 
 <!-- EVENT acp_posting_buttons_before -->
diff --git a/phpBB/adm/style/admin.css b/phpBB/adm/style/admin.css
index b0f9141d5b..2a5eacfcd7 100644
--- a/phpBB/adm/style/admin.css
+++ b/phpBB/adm/style/admin.css
@@ -1670,103 +1670,6 @@ fieldset.submit-buttons legend {
 	}
 }
 
-/* Mentions and mention dropdown
----------------------------------------- */
-.mention {
-	font-weight: bold;
-}
-
-.mention-container {
-	text-align: left;
-	background-color: #ffffff;
-	border-radius: 2px;
-	box-shadow:
-		0 3px 1px -2px rgba(0, 0, 0, 0.2),
-		0 2px 2px 0 rgba(0, 0, 0, 0.14),
-		0 1px 5px 0 rgba(0, 0, 0, 0.12);
-	position: absolute;
-	z-index: 999;
-	overflow: auto; /* placed here for list to scroll with arrow key press */
-	max-height: 200px;
-	transition: all 0.2s ease;
-}
-
-.rtl .mention-container {
-	text-align: right;
-}
-
-.mention-list {
-	margin: 0;
-	padding: 0;
-	list-style-type: none;
-}
-
-.mention-media {
-	color: #757575;
-	display: inline-flex;
-	flex-shrink: 0;
-	justify-content: center;
-	align-items: center;
-	margin-right: 8px;
-	margin-left: 0;
-}
-
-.rtl .mention-media {
-	margin-right: 0;
-	margin-left: 16px;
-}
-
-.mention-media-avatar {
-	width: 40px;
-	height: 40px;
-}
-
-.mention-item {
-	font-size: 16px;
-	font-weight: 400;
-	line-height: 1.5;
-	letter-spacing: 0.04em;
-	border-bottom: 1px solid #dddddd;
-	color: #212121;
-	position: relative;
-	display: flex;
-	overflow: hidden;
-	justify-content: flex-start;
-	align-items: center;
-	padding: 8px;
-	cursor: pointer;
-}
-
-.mention-item:hover,
-.mention-item.is-active {
-	text-decoration: none;
-	background-color: #eeeeee;
-	color: #2d80d2;
-}
-
-.mention-item:hover .mention-media-avatar,
-.mention-item.is-active .mention-media-avatar {
-	color: #2d80d2;
-}
-
-.mention-name,
-.mention-rank {
-	display: block;
-}
-
-.mention-name {
-	line-height: 1.25;
-	margin-right: 20px; /* needed to account for scrollbar bug on Firefox for Windows */
-}
-
-.mention-rank {
-	font-size: 14px;
-	font-weight: 400;
-	line-height: 1.2871;
-	letter-spacing: 0.04em;
-	color: #757575;
-}
-
 /* Input field styles
 ---------------------------------------- */
 input.radio,
diff --git a/phpBB/adm/style/mentions_templates.html b/phpBB/adm/style/mentions_templates.html
deleted file mode 100644
index 23015b03e0..0000000000
--- a/phpBB/adm/style/mentions_templates.html
+++ /dev/null
@@ -1,6 +0,0 @@
-<template data-id="mention-media-span"><span class="mention-media"></span></template>
-<template data-id="mention-media-avatar-img"><img class="avatar mention-media-avatar" src="" alt=""></template>
-<template data-id="mention-name-span"><span class="mention-name"></span></template>
-<template data-id="mention-default-avatar"><svg class="mention-media-avatar" xmlns="http://www.w3.org/2000/svg" viewbox="0 0 24 24"><path fill-rule="evenodd" d="M12,19.2C9.5,19.2 7.29,17.92 6,16C6.03,14 10,12.9 12,12.9C14,12.9 17.97,14 18,16C16.71,17.92 14.5,19.2 12,19.2M12,5A3,3 0 0,1 15,8A3,3 0 0,1 12,11A3,3 0 0,1 9,8A3,3 0 0,1 12,5M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12C22,6.47 17.5,2 12,2Z"/></svg></template>
-<template data-id="mention-default-avatar-group"><svg class="mention-media-avatar" xmlns="http://www.w3.org/2000/svg" viewbox="0 0 24 24"><path fill-rule="evenodd" d="M16 11c1.66 0 2.99-1.34 2.99-3S17.66 5 16 5c-1.66 0-3 1.34-3 3s1.34 3 3 3zm-8 0c1.66 0 2.99-1.34 2.99-3S9.66 5 8 5C6.34 5 5 6.34 5 8s1.34 3 3 3zm0 2c-2.33 0-7 1.17-7 3.5V19h14v-2.5c0-2.33-4.67-3.5-7-3.5zm8 0c-.29 0-.62.02-.97.05 1.16.84 1.97 1.97 1.97 3.45V19h6v-2.5c0-2.33-4.67-3.5-7-3.5z"/></svg></template>
-<template data-id="mention-rank-span"><span class="mention-rank"></span></template>