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 are regrouped in their own data structure (IStyle
interface).
UIElements 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.
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;
}
The USS syntax matches the W3C specifications for CSS3. UIElements uses the ExCSS open source parser to parse USS declarations. The ExCSS open source parser has its own test suite.
You can attach a Unity style sheet (USS) to any visual element. Style rules apply to the visual element and all of its descendants. Style sheets are also re-applied automatically when necessary.
Use the AddStyleSheetPath()
method to associate a USS to a visual element. You must also provide the AddStyleSheetPath()
method with the relative path to the enclosing folder. For Unity to recognize the USS file, it must be placed in the Resources
or Editor Default Resources
folder, within the Assets
folder.
If you modify a USS file while the EditorWindow
is running, style changes are applied immediately.
Once a style sheet is defined, it can be applied to a UIElements tree of visual elements.
During this process, selectors are matched against elements to resolve which properties are applied from the USS file. If a selector matches an element, the style declarations are applied to the element.
For example, the following rule matches any Button
object:
Button {
width: 200px;
}
You attach style sheets to a subtree with the VisualElement.AddStyleSheetPath()
method.
UIElements use the following criteria to match a visual element with its style rule:
name
property that is a stringThese 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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