chore(ui): title gray background.

HMCL/src/main/java/org/jackhuang/hmcl/ui/decorator/DecoratorSkin.java

@@ -158,6 +158,7 @@ public class DecoratorSkin extends SkinBase<Decorator> {
                 container.backgroundProperty().unbind();
                 container.setBackground(null);
                 titleContainer.getStyleClass().remove("background");
+                titleContainer.getStyleClass().add("gray-background");
                 container.getChildren().remove(drawerPane);
                 wrapper.getChildren().add(0, drawerPane);
             } else {
@@ -165,6 +166,7 @@ public class DecoratorSkin extends SkinBase<Decorator> {
                 wrapper.backgroundProperty().unbind();
                 wrapper.setBackground(null);
                 titleContainer.getStyleClass().add("background");
+                titleContainer.getStyleClass().remove("gray-background");
                 wrapper.getChildren().remove(drawerPane);
                 container.getChildren().add(0, drawerPane);
             }

HMCL/src/main/resources/assets/css/root.css

@@ -522,6 +522,10 @@
     -fx-text-fill: WHITE;
 }
 
+.jfx-tool-bar.gray-background Label {
+    -fx-text-fill: BLACK;
+}
+
 .jfx-tool-bar .jfx-options-burger {
     -fx-padding: 22px;
 }