Introduction to Feathers UI themes

A theme packages up styling code into a single unit that may be used to modify the appearance of all Feathers UI components in the same project. One advantage of using a theme is that it keeps styling code from getting mixed up with other logic throughout a project's code. This separation helps make a project more maintainable. A theme also makes it easier to share styles among multiple related projects or to more easily swap out one design for another when a project needs a fresh coat of paint.

Feathers UI provides a default theme, named Steel, which provides default styles to all of the core UI components. If a design requires a different appearance for UI components, it's possible to create a custom theme. Custom themes may completely replace all of the styles from the default theme, or they may enhance the default theme with some extra variants — falling back to the defaults when no customization is required.

While placing all styling code inside the theme is encouraged, this is not a strict requirement. You can style any UI component manually, from anywhere in your project. Styling properties that are set outside of the theme will take precedence over style properties that are set inside of the theme.


Any UI component may be given a variant, which allows multiple instances to to behave the same, but to give some different appearances. For instance, the Label component has two built-in variants, Label.VARIANT_HEADING and Label.VARIANT_DETAIL. A heading label is usually displayed in a slightly larger font size than a regular label, and it is meant for more prominent text, such as a title. Similarly, a detail label is usually displayed in a smaller font size, perhaps with a lighter color, for less prominent text.

Set the variant property to specify that a UI component instance should be styled as a specific variant.

var label = new Label();
label.variant = Label.VARIANT_HEADING;

While some variants are built-in, like the heading and detail variants for labels, custom variants may be created too. The variant property is a string, and any value may be used. Inside a custom theme, that variant may be referenced to provide custom styles.

Instantiating a custom theme

If you create or download a custom theme, using it is generally as simple as calling Theme.setTheme() in your project's entry point.

class MyApp extends Application {
    public function new() {
        Theme.setTheme(new MyCustomTheme());

If you're using the Application component, that should be before the call to the super constructor. If you're not using the Application component, instantiate the custom theme before creating all Feathers UI components.

Excluding an instance from the theme

(Advanced) Set the themeEnabled property of a UI component instance to false to exclude it from the theme's styles (including the default theme).

var button = new Button();
button.themeEnabled = false;
button.backgroundSkin = new RectangleSkin(SolidColor(0xCCCCCC), SolidColor(1.0, 0x000000));
button.textFormat = new TextFormat("_sans", 14, 0x000000);

Since the theme won't provide default styles to the instance, be sure to provide custom styles to replace the defaults.

Disabling the default theme

(Advanced) When a custom theme is used, the default theme will always be available as a fallback option, because a custom theme is not required to customize the styles of every type of UI component.

It's not encouraged, but if you prefer to completely disable the default theme, the feathersui_disable_default_theme define may be specified in your OpenFL project.xml file.

<haxedef name="feathersui_disable_default_theme"/>

You might do this to save on final output file size, if you are certain that your custom theme provides all of the styles that you need, and your project never needs to fall back to the default theme.