A Unity Style Sheet (USS) is a text file recognized as an asset that supports style rules. The USS text file must have the .uss extension.
You can use USS files to define the appearance and styles for the UI elements in your games and applications. USS provides a way to separate the appearance and styling of UI elements from the rest of the code, making it easier to manage and maintain the look and feel of an application.
With USS, you can define styles for buttons, labels, images, and other UI elements in a separate USS file, and then apply these styles in your game or application code. This makes it possible to change the appearance of your application by modifying the USS file, without having to make changes to the code.
A USS consists of the following:
The following is the general syntax of a style rule:
selector {
property1: value;
property2: value;
}
When you define a style sheet, you can apply it to a visual tree. Selectors match against elements to resolve which properties apply from the USS file. If a selector matches an element, the style declarations apply to the element.
例如，以下规则匹配任何 Button 对象：
Button {
width: 200px;
}
USS supports several types of simple and complex selectors that match elements based on different criteria, such as the following:
name 属性USS also supports pseudo classes that you can use with selectors to target elements that are in a specific state or select the :root element.
If an element matches more than one selector, USS applies the styles from whichever selector takes precedence.
Note: All selectors are case-sensitive.
USS supports a set of simple selectors that are analogous, but not identical, to simple selectors in CSS. The following table provides a quick reference of USS simple selectors.
| Selector type | Syntax | Matches |
|---|---|---|
| Type selector | Type {...} |
Elements of a specific C# or visual element type. |
| Class selector | .class {...} |
Elements with an assigned USS class. |
| Name selector | #name {..} |
Elements with an assigned name attribute. |
| Universal selector | * {...} |
Any elements. |
USS supports a subset of CSS complex selectors. The following table provides a quick reference of USS complex selectors.
| Selector type | Syntax | Matches |
|---|---|---|
| Descendant selector | selector1 selector2 {...} |
Elements that are the descendant of another element in the visual tree. |
| Child selector | selector1 > selector2 {...} |
Elements that are the children of another element in the visual tree. |
| Multiple selector | selector1selector2 {...} |
Elements that match all the simple selectors. |
You can connect styles to elements by the following methods:
style properties or add a USS style sheet to the styleSheet property with selectors matching an element. For more information, refer to Apply styles in C# scripts.