<dependency> <groupId>com.vaadin</groupId> <artifactId>vaadin-core</artifactId> <version>14.6.8</version> </dependency> <dependency> <groupId>com.vaadin</groupId> <artifactId>vaadin-lumo-styles</artifactId> <version>14.6.8</version> </dependency> groovy implementation 'com.vaadin:vaadin-core:14.6.8' implementation 'com.vaadin:vaadin-lumo-styles:14.6.8' Button button = new Button("Click me"); button.addClassName("primary"); String css = ":root { --lumo-primary-color: #FF0000; --lumo-error-color: #FF0000; }"; UI.getCurrent().getPage().executeJs("var style = document.createElement('style'); " + "style.innerHTML = '" + css + "'; " + "document.head.appendChild(style);");