Fix highlights for toolbar buttons to be more visible

app/gui/NavigableToolButton.qml

@@ -2,8 +2,27 @@ import QtQuick 2.0
 import QtQuick.Controls 2.2
 
 ToolButton {
+    property string iconSource
+
     activeFocusOnTab: true
 
+    // FIXME: We're using an Image here rather than icon.source because
+    // icons don't work on Qt 5.9 LTS.
+    Image {
+        id: image
+        source: iconSource
+        anchors.centerIn: parent.background
+        sourceSize {
+            width: parent.background.width * 1.10
+            height: parent.background.height * 1.10
+        }
+    }
+
+    // This determines the size of the Material highlight. We increase it
+    // from the default because we use larger than normal icons for TV readability.
+    background.width: (parent.height - parent.anchors.bottomMargin - parent.anchors.topMargin) * 0.60
+    background.height: (parent.height - parent.anchors.bottomMargin - parent.anchors.topMargin) * 0.60
+
     Keys.onReturnPressed: {
         clicked()
     }