This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

In Mozilla applications, the -moz-outline-radius-topleft CSS property can be used to round the top-left corner of an element's outline.


The value of -moz-outline-radius-topleft is either a CSS <length> or a percentage of the corresponding dimensions of the border box. The calc() function may be used as well.


The radius of the circle defining the curvature of the top and left edges of the element, specified as a CSS <length>.
The radius of the circle defining the rounding of the top-left corner of the element, specified as the percentages of the top and left sides of the border box.

Formal definition

Initial value 0
Applies to all elements
Inherited no
Percentages refer to the corresponding dimension of the border box
Computed value as specified
Animation type a length, percentage or calc();

Formal syntax


<outline-radius> = <length> | <percentage>


The example below will not display the desired effect if you are viewing this in a browser other than Firefox.


<p>Look at this paragraph's top-left corner.</p>


p {
  margin: 5px;
  border: solid cyan;
  outline: dotted red;
  -moz-outline-radius-topleft: 2em;



Not part of any standard.

Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
-moz-outline-radius-topleft No No 1 No No No
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
-moz-outline-radius-topleft No No 4 No No No

See also

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