Tabs theme, even/odd color, no gaps between tabs

src/qml/Base/HTabBar.qml

@@ -0,0 +1,7 @@
+import QtQuick 2.12
+import QtQuick.Controls 2.12
+
+TabBar {
+    spacing: 0
+    position: TabBar.Header
+}

src/qml/Base/HTabButton.qml

@@ -32,7 +32,10 @@ TabButton {
     readonly property alias iconItem: contentItem.icon
     readonly property alias label: contentItem.label
 
-    property color backgroundColor: theme.controls.tab.background
+    property color backgroundColor:
+        TabBar.index % 2 == 0 ?
+        theme.controls.tab.background : theme.controls.tab.alternateBackground
+
     property bool loading: false
 
     property HToolTip toolTip: HToolTip {