USS selectors
USS supported properties

Properties types

Built-in vs Custom properties

When using USS, you can specify values for built-in VisualElement properties or for custom properties in your UI code.

In addition of reading their values from USS files, built-in property values can be assigned to in C#, using the C# properties of VisualElement. Values assigned in C# override values from a Unity style sheet (USS).

You can extend USS with the Custom Properties API.

Property values

This section lists the supported types.


The following keywords have special meaning:

  • auto
  • inherit
  • unset
  • true
  • false
  • none

Limitation: The keywords auto, inherit, and unset are imported correctly, but are not supported at runtime.

Numeric properties

UIElements does not support units. All property types are assumed to be specified in pixels.

Numeric values are floating points or integer literals. For example: flex:1.0 or width:200. Numeric values are stored as floating-point numbers, including integer literals.


Enumerations are only supported for enum-based, built-in properties. Enumerations provide a readable name instead of a number. For example: position-type:absolute.


UIElements supports the following literal color values and functions:

  • A Hexadecimal value : #FFFF00 (rgba one byte per channel), #0F0 (rgb)
  • The RGB function : rgb(255, 255, 0)
  • The RGBA function : rgba(255, 255, 0, 1.0)
  • The HSL function : hsl(0, 100%, 50%)


You can reference assets with either the resource() or url() functions. For example, specify background-image: resource("Images/img.png") to specify the img.png in the Images directory as the background image. Referenced assets are resolved during import.

The resource() function accepts files located under either the Resources folder or the Editor Default Resources folder, with the following caveats:

  • If the file is located under the Resources folder, do not include the file extension. For example: background-image: resource("Images/my-image").
  • If the file is located under Editor Default Resources, you must include the file extension. For example: background-image: resource("Images/default-image.png").

The url() function expects the file path to be relative to either the project root or the folder containing the USS file. You must include the file extension. For example: background-image: url("Images/my-image.png").

For textures, if a file has a version with a @2x suffix, this file is automatically loaded for retina or High DPI screens.


Use quotes to specify a string value. For example: my-property: "foo".

USS selectors
USS supported properties