diff --git a/Themes/default/css/attachments.css b/Themes/default/css/attachments.css
index 8e46edd4c5..211b2bb31e 100644
--- a/Themes/default/css/attachments.css
+++ b/Themes/default/css/attachments.css
@@ -51,8 +51,8 @@ div#post_attachments_area.roundframe {
 	box-shadow: none;
 }
 #post_attachments_area #postAttachment .attached {
-	border-right: 1px dotted #ddd;
-	border-top: 1px dotted #ddd;
+	border-right: 1px dotted var(--attachment-item-border-color);
+	border-top: 1px dotted var(--attachment-item-border-color);
 	padding-top: 9px;
 	width: 200px;
 	position: relative;
@@ -173,7 +173,7 @@ div#post_attachments_area.roundframe {
 	min-height: initial;
 }
 #post_attachments_area #attachment_upload.dz-drag-hover {
-	border-color: #557ea0;
+	border-color: var(--attachment-dropzone-border-color_hover);
 }
 #post_attachments_area .dz-clickable {
 	cursor: pointer;
diff --git a/Themes/default/css/calendar.rtl.css b/Themes/default/css/calendar.rtl.css
index 262239864f..976b0be219 100644
--- a/Themes/default/css/calendar.rtl.css
+++ b/Themes/default/css/calendar.rtl.css
@@ -8,8 +8,8 @@
 	margin: 0 0 0 1%;
 }
 #main_grid table.weeklist td.windowbg {
-	border-left: 2px solid #fff;
-	border-bottom: 2px solid #fff;
+	border-left: 2px solid var(--calendar-weeklist-border-color);
+	border-bottom: 2px solid var(--calendar-weeklist-border-color);
 }
 #main_grid img.calendar_icon {
 	float: right;
@@ -18,6 +18,6 @@
 #main_grid table.weeklist td.weekdays {
 	text-align: left;
 	vertical-align: middle;
-	border-right: 2px solid #fff;
-	border-bottom: 2px solid #fff;
+	border-right: 2px solid var(--calendar-weeklist-border-color);
+	border-bottom: 2px solid var(--calendar-weeklist-border-color);
 }
\ No newline at end of file
diff --git a/Themes/default/css/dark.css b/Themes/default/css/dark.css
index 48b84a7d1a..37740b8605 100644
--- a/Themes/default/css/dark.css
+++ b/Themes/default/css/dark.css
@@ -538,6 +538,29 @@
 	/** Theme Picker **/
 	--picktheme-selected-bg:                          hsl(var(--primary-color-hue), 28%, 24%);
 
+	/** Mentions **/
+	--mentions-bg:                                    var(--dark-bg-3);
+	--mentions-border-color:                          var(--dark-line-strong);
+	--mentions-box-shadow:                            0 0 5px rgba(0, 0, 0, 0.5);
+	--mentions-item-bg:                               var(--dark-bg-2);
+	--mentions-item-bg_current:                       hsl(225, 55%, 42%);
+	--mentions-item-border-color:                     var(--dark-line);
+	--mentions-item-color:                            var(--dark-ink);
+
+	/** Shorthand Borders **/
+	--attachment-dropzone-border-color_hover:         hsl(var(--primary-color-hue), 45%, 55%);
+	--attachment-item-border-color:                   var(--dark-line);
+	--buttonrow-border-color:                         var(--dark-line);
+	--calendar-weeklist-border-color:                 var(--dark-bg-1);
+	--detailedinfo-border-color:                      var(--dark-line);
+	--draftoptions-border-color_left:                 var(--dark-line-strong);
+	--draftoptions-item-border-color:                 var(--dark-line);
+	--errorfile-current-border-color:                 rgba(255, 255, 255, 0.2);
+	--innerwrap-border-color:                         var(--dark-line);
+	--listposts-border-color:                         var(--dark-line);
+	--mobileaction-item-border-color:                 var(--dark-line);
+	--upcontain-lastpost-border-color:                var(--dark-line);
+
 	/** Admin **/
 	/* The permission grid is the one place a background alone carries the
 	/* meaning - deny, allow, custom, unchanged - so those six keep their hues
diff --git a/Themes/default/css/index.css b/Themes/default/css/index.css
index 2f2e70e177..32c170b33c 100644
--- a/Themes/default/css/index.css
+++ b/Themes/default/css/index.css
@@ -1292,7 +1292,7 @@ h1.forumtitle {
 }
 h1.forumtitle a {
 	color: var(--forumtitle-link-color);
-	text-shadow: 1px 1px 1px rgba(0, 0, 0, 0.3);
+	text-shadow: var(--forumtitle-link-text-shadow);
 }
 /* Float these items to the right */
 #siteslogan, img#smflogo {
@@ -1316,7 +1316,7 @@ img#smflogo {
 	display: flex;
 	justify-content: space-between;
 	align-items: center;
-	border-bottom: 1px solid #bbb;
+	border-bottom: 1px solid var(--innerwrap-border-color);
 	margin-bottom: 12px;
 	padding: 12px 10px 2px 10px;
 }
@@ -1959,8 +1959,8 @@ tr.windowbg td, tr.bg td, .table_grid tr td {
 }
 .errorfile_table td.current {
 	font-weight: bold;
-	border-top: 1px solid rgba(0, 0, 0, 0.2);
-	border-bottom: 1px solid rgba(0, 0, 0, 0.2);
+	border-top: 1px solid var(--errorfile-current-border-color);
+	border-bottom: 1px solid var(--errorfile-current-border-color);
 	border-width: 1px 0 1px 1px;
 	background: var(--errorfile-bg_current);
 }
@@ -2513,7 +2513,7 @@ dl {
 	margin-left: 25px;
 }
 .list_posts {
-	border-top: 1px solid #ddd;
+	border-top: 1px solid var(--listposts-border-color);
 	box-shadow: var(--listposts-box-shadow);
 	padding-top: 1em;
 	margin-top: 1em;
@@ -3673,13 +3673,13 @@ form#postmodify .roundframe {
 #post_draft_options {
 	background: var(--draftoptions-bg);
 	border: 1px solid var(--draftoptions-border-color);
-	border-left: 1px solid #bbb;
+	border-left: 1px solid var(--draftoptions-border-color_left);
 	border-top: none;
 	border-radius: 0 0 4px 4px;
 }
 #post_draft_options .settings dd, #post_draft_options .settings dt {
 	width: 50%;
-	border-top: 1px solid #e4e4e4;
+	border-top: 1px solid var(--draftoptions-item-border-color);
 	padding: 5px 10px;
 	margin: 0;
 }
diff --git a/Themes/default/css/profile.css b/Themes/default/css/profile.css
index c54074e9dd..8a43434043 100644
--- a/Themes/default/css/profile.css
+++ b/Themes/default/css/profile.css
@@ -66,7 +66,7 @@
 	overflow: auto;
 	margin: 0 0 18px 0;
 	padding: 0 0 15px 0;
-	border-bottom: 1px #ccc solid;
+	border-bottom: 1px var(--detailedinfo-border-color) solid;
 }
 
 #detailedinfo dt, #tracking dt {
diff --git a/Themes/default/css/responsive.css b/Themes/default/css/responsive.css
index ea9261c689..61293d09a6 100644
--- a/Themes/default/css/responsive.css
+++ b/Themes/default/css/responsive.css
@@ -72,7 +72,7 @@
 		margin: 0 auto;
 	}
 	#mobile_action .notify_dropdown a {
-		border-bottom: 1px solid #999;
+		border-bottom: 1px solid var(--mobileaction-item-border-color);
 	}
 	#mobile_action .notify_dropdown a:last-of-type {
 		border-bottom: none;
@@ -194,7 +194,7 @@
 		min-height: 2em;
 	}
 	.up_contain .lastpost {
-		border-top: 1px solid #ddd;
+		border-top: 1px solid var(--upcontain-lastpost-border-color);
 		min-height: initial;
 	}
 	.lastpost p {
diff --git a/Themes/default/css/rtl.css b/Themes/default/css/rtl.css
index 6dc4fc3d9e..1be7dec6ad 100644
--- a/Themes/default/css/rtl.css
+++ b/Themes/default/css/rtl.css
@@ -201,7 +201,7 @@ ul.quickbuttons li {
 }
 .buttonrow .button:first-child {
 	border-radius: 0;
-	border-right: 1px solid #ccc;
+	border-right: 1px solid var(--buttonrow-border-color);
 }
 
 .post_verification #verification_control {
diff --git a/Themes/default/css/variables.css b/Themes/default/css/variables.css
index a7051b0d44..11ef5e503a 100644
--- a/Themes/default/css/variables.css
+++ b/Themes/default/css/variables.css
@@ -792,4 +792,46 @@
 	--editor-popup-container-bg:                      #f5f5f5;
 	--editor-tablegrid-bg_active:                     #85a1b7;
 	--editor-tablegrid-border-color:                  #85a1b7;
+
+	/* Borders written as a shorthand rather than as a -color property, so
+	/* the sweep that tokenised the rest of the theme did not see them. */
+	/** Shorthand Borders **/
+	--attachment-dropzone-border-color_hover:         #557ea0;
+	--attachment-item-border-color:                   #ddd;
+	--buttonrow-border-color:                         #ccc;
+	--calendar-weeklist-border-color:                 #fff;
+	--detailedinfo-border-color:                      #ccc;
+	--draftoptions-border-color_left:                 #bbb;
+	--draftoptions-item-border-color:                 #e4e4e4;
+	--errorfile-current-border-color:                 rgba(0, 0, 0, 0.2);
+	--forumtitle-link-text-shadow:                    1px 1px 1px rgba(0, 0, 0, 0.3);
+	--innerwrap-border-color:                         #bbb;
+	--listposts-border-color:                         #ddd;
+	--mobileaction-item-border-color:                 #999;
+	--upcontain-lastpost-border-color:                #ddd;
+
+	/* atwho.css already gives each of these a fallback, so the mentions list
+	/* has never looked wrong. But a token that is never declared cannot be
+	/* overridden either, which is what kept the list light in dark mode. Each
+	/* value here is the fallback it is declared from. */
+	/** Mentions **/
+	--mentions-bg:                                    #fff;
+	--mentions-border-color:                          hsl(0, 0%, 85%);
+	--mentions-border-radius:                         1px;
+	--mentions-border-style:                          solid;
+	--mentions-border-width:                          1px;
+	--mentions-box-shadow:                            0 0 5px rgba(0, 0, 0, 0.1);
+	--mentions-item-bg:                               #f2f2f2;
+	--mentions-item-bg_current:                       hsl(225, 100%, 60%);
+	--mentions-item-border-color:                     hsl(0, 0%, 85%);
+	--mentions-item-border-style:                     solid;
+	--mentions-item-border-width:                     0 0 1px;
+	--mentions-item-color:                            hsl(0, 0%, 20%);
+	--mentions-item-color_current:                    #fff;
+	--mentions-item-cursor:                           pointer;
+	--mentions-item-font-size:                        .95em;
+	--mentions-item-font-size_current:                .95em;
+	--mentions-item-font-weight:                      normal;
+	--mentions-item-font-weight_current:              normal;
+	--mentions-width:                                 120px;
 }