Don't set background color if zebra pattern is enabled on trees

On macOS setting "linesVisible" to true creates an zebra styled pattern
on the tree. If we now set the background color via CSS
on this tree that pattern would be gone. Setting the background color
via CSS on a tree that has "linesVisible" to false does not do any harm.

Author: BeckerWdf

bundles/org.eclipse.e4.ui.css.swt/src/org/eclipse/e4/ui/css/swt/properties/css2/CSSPropertyBackgroundSWTHandler.java

@@ -23,13 +23,15 @@
 import org.eclipse.e4.ui.css.swt.helpers.CSSSWTImageHelper;
 import org.eclipse.e4.ui.css.swt.helpers.SWTElementHelpers;
 import org.eclipse.e4.ui.css.swt.properties.GradientBackgroundListener;
+import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
 import org.eclipse.swt.custom.CTabItem;
 import org.eclipse.swt.graphics.Color;
 import org.eclipse.swt.graphics.Image;
 import org.eclipse.swt.widgets.Button;
 import org.eclipse.swt.widgets.Control;
 import org.eclipse.swt.widgets.ToolItem;
+import org.eclipse.swt.widgets.Tree;
 import org.eclipse.swt.widgets.Widget;
 import org.w3c.dom.css.CSSValue;
 
@@ -75,6 +77,11 @@ public void applyCSSPropertyBackgroundColor(Object element, CSSValue value,
 				// ToolItem prevents itself from repaints if the same color is set
 				((ToolItem) widget).setBackground(newColor);
 			} else if (widget instanceof Control) {
+				if ("cocoa".equals(SWT.getPlatform()) && widget instanceof Tree tree && tree.getLinesVisible()) {
+					// on macOS "linesVisible" creates zebra-styled pattern.
+					// If we now would set the background color this zebra pattern would be gone.
+					break;
+				}
 				GradientBackgroundListener.remove((Control) widget);
 				CSSSWTColorHelper.setBackground((Control) widget, newColor);
 				CompositeElement.setBackgroundOverriddenByCSSMarker(widget);