Pseudo-classes

A pseudo-class narrows a selector’s scope so it only matches elements when they enter a specific state.

Append a pseudo-class to a simple selector to match specific elements when they’re in a specific state. For example, the following USS rule uses the :hover pseudo-class to change the color of Button elements when a user hovers the pointer over them.

Button:hover {
    background-color: palegreen;
}

Supported pseudo-classes

The table below lists the pseudo classes that Unity supports. You cannot extend pseudo-classes or create custom ones.

Chaining pseudo-classes

You can chain pseudo-classes together to apply the same style for multiple concurrent states. For example, the following USS rule chains the :checked and :hover pseudo-classes together to change the color of checked Toggle elements when a user hovers the pointer over them.

Toggle:checked:hover {
  background-color: yellow;
}

When the toggle is checked, but the pointer isn’t hovering over it, the selector no longer matches.

The root pseudo-class

The :root pseudo class matches the highest element in a visual tree. It’s slightly different from other supported pseudo-classes because you use it by itself to define default styles for the elements the style sheet affects.

For example, the following USS rule sets a default font. Any element that doesn’t get its font from a more specific style rule uses that font.

:root {
  -unity-font: url("../Resources/fonts/OpenSans-Regular.ttf");
}

A common use for the :root selector is to declare “global” variables (custom properties), that other style rules can use instead of specific values.