Visual fixes for Linux

Author: Stefterv

app/src/processing/app/platform/LinuxPlatform.java

@@ -31,6 +31,8 @@
 import processing.app.Preferences;
 import processing.core.PApplet;
 
+import javax.swing.*;
+
 
 public class LinuxPlatform extends DefaultPlatform {
   String homeDir;
@@ -39,6 +41,9 @@ public class LinuxPlatform extends DefaultPlatform {
   public void initBase(Base base) {
     super.initBase(base);
 
+    JFrame.setDefaultLookAndFeelDecorated(true);
+    System.setProperty("flatlaf.menuBarEmbedded", "true");
+
     // Set X11 WM_CLASS property which is used as the application
     // name by Gnome 3 and other window managers.
     // https://github.com/processing/processing/issues/2534

app/src/processing/app/ui/Editor.java

@@ -618,12 +618,10 @@ public void updateTheme() {
     toolTipWarningColor = Theme.get("errors.selection.warning.bgcolor");
     toolTipErrorColor = Theme.get("errors.selection.error.bgcolor");
 
-    if(Platform.isWindows()) {
-      UIManager.put("RootPane.background", color);
-      UIManager.put("TitlePane.embeddedForeground", Theme.getColor("editor.fgcolor"));
-      getRootPane().updateUI();
-      UIManager.put("RootPane.background", null);
-    }
+    UIManager.put("RootPane.background", color);
+    UIManager.put("TitlePane.embeddedForeground", Theme.getColor("editor.fgcolor"));
+    getRootPane().updateUI();
+    UIManager.put("RootPane.background", null);
 
     JPopupMenu popup = modePopup.getPopupMenu();
     // Cannot use instanceof because com.formdev.flatlaf.ui.FlatPopupMenuBorder