Each VisualElement
includes style properties that set the dimensions of the element and how the element is drawn on screen, such as backgroundColor
or borderColor
.
Style properties are either set in C# or from a style sheet. Style properties have their own data structure (IStyle
interface).
UI Toolkit supports style sheets written in USS (Unity style sheet). USS files are text files inspired by Cascading Style Sheets (CSS) from HTML. The USS format is similar to CSS, but USS includes overrides and customizations to work better with Unity.
This section includes details on USS, its syntax, and its differences when compared to CSS.
For a quick reference of supported USS properties, see the USS properties reference.
The fundamental building blocks of a Unity style sheet (USS) are as follows :
.uss
extension.The general syntax of a style rule is :
selector {
property1:value;
property2:value;
}
You can attach a Unity style sheet (USS) to any visual element. Style rules apply to the visual element and all its descendants. Style sheets are also re-applied automatically when necessary.
Load StyleSheet
objects with standard Unity APIs such as AssetDatabase.Load()
or Resources.Load()
. Use the VisualElement.styleSheets.Add()
method to attach style sheets to visual elements.
If you modify a USS file while the EditorWindow
is running, style changes are applied immediately.
The process of style application is transparent to a developer using UI Toolkit. Style sheets are re-applied automatically when needed (hierarchy changes, stylesheet reload).
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.
For example, the following rule matches any Button
object:
Button {
width: 200px;
}
UI Toolkit uses the following criteria to match a visual element with its style rule:
name
property that’s a string.These traits can be used in selectors in the style sheet.
If you are familiar with CSS you can see the similarity with the HTML tag name, the id
attribute and class
attribute.
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