Remove unnecessary flag.

core/src/main/java/com/github/weisj/darklaf/components/CloseButton.java

@@ -31,13 +31,13 @@ import com.github.weisj.darklaf.ui.button.DarkButtonUI;
 class CloseButton extends JButton {
 
     protected CloseButton() {
-        putClientProperty(DarkButtonUI.KEY_NO_BACKGROUND, true);
         putClientProperty(DarkButtonUI.KEY_NO_BORDERLESS_OVERWRITE, true);
         putClientProperty(DarkButtonUI.KEY_VARIANT, DarkButtonUI.VARIANT_BORDERLESS_RECTANGULAR);
         putClientProperty(DarkButtonUI.KEY_THIN, true);
         setOpaque(false);
         setRolloverEnabled(true);
         setBorderPainted(false);
+        setContentAreaFilled(false);
         setIcon(UIManager.getIcon("CloseButton.closeIcon"));
         setDisabledIcon(UIManager.getIcon("CloseButton.closeDisabledIcon"));
         setRolloverIcon(UIManager.getIcon("CloseButton.closeHoverIcon"));

core/src/main/java/com/github/weisj/darklaf/ui/button/ButtonConstants.java

@@ -42,7 +42,6 @@ public interface ButtonConstants {
     String KEY_NO_BORDERLESS_OVERWRITE = "JButton.noBorderlessOverwrite";
     String KEY_CORNER = "JButton.cornerFlag";
     String KEY_ROUND = "JButton.round";
-    String KEY_NO_BACKGROUND = "JButton.noBackground";
 
     String KEY_LEFT_NEIGHBOUR = "JButton.leftNeighbour";
     String KEY_RIGHT_NEIGHBOUR = "JButton.rightNeighbour";
@@ -129,8 +128,4 @@ public interface ButtonConstants {
     static JComponent getNeighbour(final String key, final Component comp) {
         return PropertyUtil.getObject(comp, key, JComponent.class);
     }
-
-    static boolean isNoBackground(final AbstractButton b) {
-        return PropertyUtil.getBooleanProperty(b, KEY_NO_BACKGROUND);
-    }
 }

core/src/main/java/com/github/weisj/darklaf/ui/button/DarkButtonUI.java

@@ -286,7 +286,6 @@ public class DarkButtonUI extends BasicButtonUI implements ButtonConstants {
     }
 
     protected boolean shouldDrawBackground(final AbstractButton c) {
-        if (ButtonConstants.isNoBackground(c)) return false;
         Border border = c.getBorder();
         return c.isEnabled() && border != null && button.isContentAreaFilled();
     }

core/src/main/java/com/github/weisj/darklaf/ui/splitpane/DarkSplitPaneDivider.java

@@ -31,7 +31,6 @@ import javax.swing.plaf.UIResource;
 import javax.swing.plaf.basic.BasicSplitPaneDivider;
 
 import com.github.weisj.darklaf.icons.EmptyIcon;
-import com.github.weisj.darklaf.ui.button.DarkButtonUI;
 
 /**
  * @author Jannis Weis
@@ -122,7 +121,7 @@ public class DarkSplitPaneDivider extends BasicSplitPaneDivider {
         protected OneTouchButton() {
             setMinimumSize(new Dimension(ONE_TOUCH_SIZE, ONE_TOUCH_SIZE));
             setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
-            putClientProperty(DarkButtonUI.KEY_NO_BACKGROUND, true);
+            setContentAreaFilled(false);
             setRequestFocusEnabled(false);
             setBorderPainted(false);
             setFocusPainted(false);

core/src/test/java/ui/button/AbstractButtonDemo.java

@@ -100,10 +100,10 @@ public abstract class AbstractButtonDemo<T extends AbstractButton> implements Co
                 addActionListener(e -> button.putClientProperty(DarkButtonUI.KEY_ALT_ARC, isSelected()));
             }
         });
-        controlPanel.add(new JCheckBox(DarkButtonUI.KEY_NO_BACKGROUND) {
+        controlPanel.add(new JCheckBox("Content area filled") {
             {
-                setSelected(false);
+                setSelected(button.isContentAreaFilled());
-                addActionListener(e -> button.putClientProperty(DarkButtonUI.KEY_NO_BACKGROUND, isSelected()));
+                addActionListener(e -> button.setContentAreaFilled(isSelected()));
             }
         });
         controlPanel.add(new JCheckBox("Button.defaultButtonFollowsFocus") {

windows/src/main/java/com/github/weisj/darklaf/platform/windows/ui/WindowsTitlePane.java

@@ -389,12 +389,12 @@ public class WindowsTitlePane extends CustomTitlePane {
         windowIconButton = new JButton();
         windowIconButton.putClientProperty("JButton.noShadowOverwrite", true);
         windowIconButton.setComponentPopupMenu(createMenu());
-        windowIconButton.putClientProperty("JButton.noBackground", true);
         windowIconButton.addActionListener(e -> windowIconButton.getComponentPopupMenu()
                                                                 .show(windowIconButton,
                                                                       windowIconButton.getWidth() / 2,
                                                                       windowIconButton.getHeight() / 2));
         windowIconButton.setFocusable(false);
+        windowIconButton.setContentAreaFilled(false);
         windowIconButton.setBorderPainted(false);
         return windowIconButton;
     }