fix(ui): address main window KDE HIG findings

src/qml/MpvVideo.qml

@@ -30,6 +30,9 @@ MpvItem {
         setPropertyAsync("sub-outline-size", QtPotatoSettings.subtitleOutlineSize)
     }
 
+    Kirigami.Theme.colorSet: Kirigami.Theme.Complementary
+    Kirigami.Theme.inherit: false
+
     loadUserConfig: QtPotatoSettings.loadMpvConfig
 
     // Set once the saved volume is applied; mpv reports its default volume before that.
@@ -55,7 +58,7 @@ MpvItem {
 
     Rectangle {
         anchors.fill: parent
-        color: "black"
+        color: Kirigami.Theme.backgroundColor
         visible: !root.fileLoaded
         z: -1
     }
@@ -95,6 +98,7 @@ MpvItem {
         onExited: root.pointerLeft()
 
         onPressed: mouse => {
+            root.forceActiveFocus(Qt.MouseFocusReason)
             switch (mouse.button) {
             case Qt.LeftButton:
                 root.actions.playPause.trigger()