diff --git a/resources/common/components/MenuDropdown.less b/resources/common/components/MenuDropdown.less
index 6086ffa8e..e98e328dc 100644
--- a/resources/common/components/MenuDropdown.less
+++ b/resources/common/components/MenuDropdown.less
@@ -13,7 +13,7 @@
 		color: @color-base--subtle;
 		position: relative;
 		display: block;
-		.box-sizing( border-box );
+		box-sizing: border-box;
 
 		&:after {
 			content: '';
diff --git a/resources/common/components/MenuTabs.less b/resources/common/components/MenuTabs.less
index ac19cc6c4..91d01175d 100644
--- a/resources/common/components/MenuTabs.less
+++ b/resources/common/components/MenuTabs.less
@@ -44,7 +44,7 @@
 			// Tab separator: Border between tabs and outer right border.
 			background-position: right bottom;
 			color: @color-link;
-			.box-sizing( border-box );
+			box-sizing: border-box;
 			display: block;
 			float: left;
 			height: unit( 40 / @font-size-tabs / @font-size-browser, em );
diff --git a/resources/common/components/SearchBox.less b/resources/common/components/SearchBox.less
index d7fe3bc24..03711b3b8 100644
--- a/resources/common/components/SearchBox.less
+++ b/resources/common/components/SearchBox.less
@@ -18,7 +18,7 @@
 	width: 100%;
 	// Reduce height slightly from standard to match legacy Vector tabs.
 	height: unit( 28 / @font-size-browser / @font-size-search-input, em ); // Equals `2.15384615em`.
-	.box-sizing( border-box );
+	box-sizing: border-box;
 	border: @border-base;
 	border-radius: @border-radius-base;
 	// `padding-right` equals to `#searchbutton` width below.
diff --git a/resources/skins.vector.styles/components/LanguageButton.less b/resources/skins.vector.styles/components/LanguageButton.less
index e500cdf2f..64984dc62 100644
--- a/resources/skins.vector.styles/components/LanguageButton.less
+++ b/resources/skins.vector.styles/components/LanguageButton.less
@@ -8,7 +8,7 @@
 .vector-language-in-header-enabled .mw-portlet-lang {
 	// FIXME [review whether margin-top is needed] center vertically in heading.
 	margin-top: 2px;
-	.box-sizing( border-box );
+	box-sizing: border-box;
 	height: @height-lang-button;
 
 	.mw-ui-icon:before {
@@ -67,7 +67,7 @@
 		left: -@border-width-base;
 		right: -@border-width-base;
 		// align borders of open menu align with button
-		.box-sizing( border-box );
+		box-sizing: border-box;
 		max-height: 65vh;
 		overflow: auto;
 		border-top-width: 1px;
diff --git a/resources/skins.vector.styles/components/Sidebar.less b/resources/skins.vector.styles/components/Sidebar.less
index 982a62d26..aeef8e4b1 100644
--- a/resources/skins.vector.styles/components/Sidebar.less
+++ b/resources/skins.vector.styles/components/Sidebar.less
@@ -19,7 +19,7 @@
 	// we apply top and bottom padding.
 	padding: 8px 0 40px @padding-left-sidebar;
 	background-image: linear-gradient( to bottom, @background-color-base 0%, @background-color-secondary--modern 10%, @background-color-secondary--modern 90%, @background-color-base 100% );
-	.box-sizing( border-box );
+	box-sizing: border-box;
 
 	// Hide #p-navigation label
 	#p-navigation .vector-menu-heading {
diff --git a/resources/skins.vector.styles/components/TableOfContents.less b/resources/skins.vector.styles/components/TableOfContents.less
index e6b263379..b8ebabe92 100644
--- a/resources/skins.vector.styles/components/TableOfContents.less
+++ b/resources/skins.vector.styles/components/TableOfContents.less
@@ -9,7 +9,7 @@
 	width: @width-sidebar;
 	max-height: 75vh;
 	padding: @vertical-padding 12px @vertical-padding 32px;
-	.box-sizing( border-box );
+	box-sizing: border-box;
 	overflow: auto;
 	background-color: @border-color-sidebar;