USS properties syntax

This page introduces the common USS properties, their syntax and accepted values, and differences from CSS. For a complete list of USS properties, see USS properties reference.

USS properties use the same grammar syntax as W3C CSS documents:

• Keyword values appear as is. For example: auto, baseline.
• Basic data types appear between angle brackets ( < and >). For example: <length>, <color>.
• Non-terminals that share the same name as a property appear between angle brackets and single straight quotes ( <' and '>). For example, <'width'>.

If a property value has more than one component:

• Side-by-side words mean that all of them must occur in the given order.
• A bar (|) separates two or more alternatives: exactly one must occur.
• A double bar (||) separates two or more options: one or more must occur, in any order.
• A double ampersand (&&) separates two or more components, all of which must occur, in any order.
• Square brackets ([ ]) denote grouping.

Every type, keyword, or angle-bracketed group might be followed by modifiers:

• an asterisk (*) indicates that the preceding type, word, or group occurs zero or more times.
• a plus (+) indicates that the preceding type, word, or group occurs one or more times.
• a question mark (?) indicates that the preceding type, word, or group is optional.
• a pair of numbers in curly braces ({A,B}) indicates that the preceding type, word, or group occurs at least A and at most B times.

Box model

Dimensions

width: <length> | auto
height: <length> | auto
min-width: <length> | auto
min-height: <length> | auto
max-width: <length> | none
max-height: <length> | none

The width and height specifies the size of the element. If width is not specified, the width is based on the width of the element’s contents. If height is not specified, the height is based on the height of the element’s contents.

Margins

margin-left: <length> | auto;
margin-top: <length> | auto
margin-right: <length> | auto
margin-bottom: <length> | auto
/* Shorthand */
margin: [<length> | auto]{1,4}

Borders

border-left-width: <length>
border-top-width: <length>
border-right-width: <length>
border-bottom-width: <length>
/* Shorthand */
border-width: <length>{1,4}

Padding

padding-left: <length>
padding-top: <length>
padding-right: <length>
padding-bottom: <length>
/* Shorthand */
padding: <length>{1,4}

Differences from CSS

The alternative box model that USS uses is different from the standard CSS box model. In the standard CSS box model, width and height define the size of the content box. An element’s rendered size is the sum of its padding, border-width, and width / height values.

Unity’s model is equivalent to setting the CSS box-sizing property to border-box. See the MDN documentation for details.

Flex layout

UI Toolkit includes a layout engine that positions visual elements based on layout and styling properties. The layout engine implements a subset of Flexbox, an HTML/CSS layout system.

By default, all items are vertically placed in their container.

/* Items */
flex-grow: <number>
flex-shrink: <number>
flex-basis: <length> | auto
flex: none | [ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]
align-self: auto | flex-start | flex-end | center | stretch

/* Containers */
flex-direction: row | row-reverse | column | column-reverse
flex-wrap: nowrap | wrap | wrap-reverse
align-content: flex-start | flex-end | center | stretch
align-items: flex-start | flex-end | center | stretch
justify-content: flex-start | flex-end | center | space-between | space-around

Positioning

/* The default value is `relative` which positions the element based on its parent. 
If sets to `absolute`, the element leaves its parent layout and values are specified based on the parent bounds.*/
position: absolute | relative

/* The distance from the parent edge or the original position of the element. */
left: <length> | auto
top: <length> | auto
right: <length> | auto
bottom: <length> | auto

Background

background-color: <color>
background-image: <resource> | <url> | none
-unity-background-scale-mode: stretch-to-fill | scale-and-crop | scale-to-fit
-unity-background-image-tint-color: <color>

Slicing

When assigning a background image, you draw it with respect to a simplified 9-slice specification:

-unity-slice-left: <integer>
-unity-slice-top: <integer>
-unity-slice-right: <integer>
-unity-slice-bottom: <integer>
-unity-slice-scale: <length>

Border color

border-color: <color>

Border radius

border-top-left-radius: <length>
border-top-right-radius: <length>
border-bottom-left-radius: <length>
border-bottom-right-radius: <length>
/* Shorthand */
border-radius: <length>{1,4}

Differences from CSS

Border radius properties work almost the same in USS and CSS. For detailed information about border-radius, see the MDN documentation.

However, there are two main differences:

• Unity doesn’t support the second-radius shorthand (border-radius: (first radius values) / (second radius values);) used to create elliptical corners.
• Unity reduces border radius values to half of the element’s size in pixelsThe smallest unit in a computer image. Pixel size depends on your screen resolution. Pixel lighting is calculated at every screen pixel. More info
  See in Glossary. For example, for a 100px x 100px element, any border-radius value greater than 50px is reduced to 50px. If you use percentage (%) values for border radius properties, Unity first resolves the percentage to pixels and then reduces the border-radius value to half of the resolved pixel value. If you have different radius values for two or more corners, Unity reduces any values greater than half of the element’s size to half of the element’s size.

Appearance

overflow: hidden | visible
-unity-overflow-clip-box: padding-box | content-box
-unity-paragraph-spacing: <length>
opacity: <number>
visibility: visible | hidden
display: flex | none

The -unity-overflow-clip-box defines the clipping rectangle for the element content. The default is padding-box, the rectangle outside the padding area (the green rectangle in the box model image above); content-box represents the value inside the padding area (the blue rectangle in the box model image above).

The display default value is flex. Setting display to none removes the element. Setting the visibility to hidden hides the element, but the element still occupies space in the layout.

Differences from CSS

The USS display property supports only a small subset of the CSS display property’s available keyword values. The USS version supports keywords that work with the Yoga layout engine.

• For more information about Yoga, see Layout.
• For more information about the CSS display property, see the MDN documentation.

Text properties

Text properties set the color, font, font size, and Unity specific properties for font resource, font style, alignment, word wrap, and clipping.

color: <color>
-unity-font: <resource> | <url>
-unity-font-definition: <resource> | <url>
font-size: <number>
-unity-font-style: normal | italic | bold | bold-and-italic
-unity-text-align: upper-left | middle-left | lower-left | upper-center | middle-center | lower-center | upper-right | middle-right | lower-right
-unity-text-overflow-position: start | middle | end
white-space: normal | nowrap

-unity-text-outline-width: <length>
-unity-text-outline-color: <color>
/* Shorthand */
-unity-text-outline: <length> | <color>

Note: When setting up font in UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary Builder, the Font control in the InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
See in Glossary sets -unity-font, and the Font Asset control sets -unity-font-definition. Because -unity-font-definition takes precedence over -unity-font, if you want to use a font from the Font list, you must select None from Font Asset. Otherwise, the font you selected won’t take effect.

Cursor

Use the cursor default texture type to import a custom texture for the cursor.

cursor: [ [ <resource> | <url> ] [ <integer> <integer>]? , ] [ arrow | text | resize-vertical | resize-horizontal | link | slide-arrow | resize-up-right | resize-up-left | move-arrow | rotate-arrow | scale-arrow | arrow-plus | arrow-minus | pan | orbit | zoom | fps | split-resize-up-down | split-resize-left-right ]

Differences from CSS

In CSS, you can specify multiple optional custom cursors and a mandatory keyword in a single cursor style declaration. When you specify multiple cursors, they form a fallback chain. If the browser can’t load the first custom cursor, it tries each of the others in sequence until one of them loads or there are no more custom cursors to try. If the browser can’t load any custom cursors, it uses the keyword.

In USS, custom cursors and keywords are mutually exclusive. A cursor style declaration can only have one custom cursor or one keyword.

For detailed information about the CSS cursor property, see the MDN documentation.

Opacity

opacity: <number>

Differences from CSS

USS opacity is similar to CSS opacity. The opacity of parent elements affects the perceived opacity of child elements. The perceivability is different between USS opacity and CSS opacity.

In the following USS example, the blue square is a child of the red square. The red square has an opacity of 0.5.

.red {
    background-color: red;
    opacity: 0.5;
}

.blue {
    background-color: blue;
    left: 20px;
    top: 20px;
}

Although the blue square doesn’t have an opacity value, it has a perceived opacity of 0.5 from the red square. You can see the red square through the blue square.

In CSS, if you apply the same styles, both the red and blue squares are 50% transparent. However, you can’t see the red square through the blue square, unless you also set the opacity of blue to be less than 1.

Additional resources

• USS transform
• USS transition