Tab bar: Fix tabs on Windows & Linux

scss/components/_mainWindow.scss

@@ -90,6 +90,10 @@ toolbarpaletteitem {
 
 /* ::::: Tabs in Titlebar :::::: */
 
+#main-window:not([chromemargin]) > #titlebar {
+  display: none;
+}
+
 /**
  * For tabs in titlebar on OS X, we stretch the titlebar down so that the
  * tabstrip can overlap it.

scss/components/_tabBar.scss

@@ -4,16 +4,29 @@
 
 .tabs {
 	display: flex;
-}
 
-.tabs-holder {
-	display: flex;
+	&:before {
+		content: "";
+		width: 0px;
+		min-width: 0px;
+		border-bottom: $tab-border;
+		border-inline-end: $tab-border;
+	}
+
+	&:after {
+		content: "";
+		flex: 1 0 0%;
+		width: 100%;
+		min-width: 0px;
+		border-bottom: $tab-border;
+		border-inline-start: $tab-border;
+	}
 }
 
 .tab {
 	-moz-appearance: none;
 	max-width: 200px;
-	flex: 1;
+	flex: 1 1 200px;
 	height: 30px;
 	line-height: 30px;
 	position: relative;
@@ -24,7 +37,7 @@
 	padding: 0 30px;
 	
 	&:not(:last-child) {
-		border-right: $tab-border;
+		border-inline-end: $tab-border;
 	}
 	
 	&.selected {
@@ -56,4 +69,8 @@
 	&:hover:not(:first-child) .tab-close {
 		display: block;
 	}
-}
+
+	&:not(.selected) {
+		border-bottom: $tab-border;
+	}
+}

scss/linux/_tabBar.scss

@@ -1,3 +0,0 @@
-.tabs-holder {
-	flex: 1;
-}

scss/mac/_tabBar.scss

@@ -2,30 +2,17 @@
 	-moz-window-dragging: drag;
 }
 
-.tabs-spacer-before {
-	width: 78px;
-	border-bottom: $tab-border;
-	border-inline-end: $tab-border;
-}
-
-.tabs-spacer-after {
-	flex: 1;
-	border-inline-start: $tab-border;
-	border-bottom: $tab-border;
-}
-
 .tab {
 	-moz-window-dragging: no-drag;
 }
 
-.tab:not(.selected) {
-	border-bottom: $tab-border;
-}
+.tabs {
+	&:before {
+		width: 78px;
+		min-width: 78px;
+	}
 
-.tab:first-child {
-	border-left: 0;
+	&:after {
+		min-width: 20px;
+	}
 }
-
-.tab:last-child {
-	border-right: 0;
-}

scss/zotero-react-client-unix.scss

@@ -7,5 +7,4 @@
 @import "linux/createParent";
 @import "linux/editable";
 @import "linux/search";
-@import "linux/tabBar";
 @import "linux/tagsBox";