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border-top-left-radius

The border-top-left-radius CSS property rounds the top-left corner of an element by specifying the radius (or the radius of the semi-major and semi-minor axes) of the ellipse defining the curvature of the corner.

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The rounding can be a circle or an ellipse, or if one of the value is 0, no rounding is done and the corner is square.

A background, being an image or a color, is clipped at the border, even a rounded one; the exact location of the clipping is defined by the value of the background-clip property.

Note: If the value of this property is not set in a border-radius shorthand property that is applied to the element after the border-top-left-radius CSS property, the value of this property is then reset to its initial value by the shorthand property.

Syntax

/* the corner is a circle */
/* border-top-left-radius: radius */
border-top-left-radius: 3px;

/* the corner is an ellipse */
/* border-top-left-radius: horizontal vertical */
border-top-left-radius: 0.5em 1em;

border-top-left-radius: inherit;

/* Global values */
border-top-left-radius: inherit;
border-top-left-radius: initial;
border-top-left-radius: revert;
border-top-left-radius: revert-layer;
border-top-left-radius: unset;

With one value:

the value is a <length> or a <percentage> denoting the radius of the circle to use for the border in that corner.

With two values:

the first value is a <length> or a <percentage> denoting the horizontal semi-major axis of the ellipse to use for the border in that corner.
the second value is a <length> or a <percentage> denoting the vertical semi-major axis of the ellipse to use for the border in that corner.

Values

<length-percentage>: Denotes the size of the circle radius or the semi-major and semi-minor axes of the ellipse. As absolute length it can be expressed in any unit allowed by the CSS <length> data type. Percentages for the horizontal axis refer to the width of the box, percentages for the vertical axis refer to the height of the box. Negative values are invalid.

Formal definition

Initial value	`0`
Applies to	all elements; but User Agents are not required to apply to `table` and `inline-table` elements when `border-collapse` is `collapse`. The behavior on internal table elements is undefined for the moment.. It also applies to `::first-letter`.
Inherited	no
Percentages	refer to the corresponding dimension of the border box
Computed value	two absolute `<length>`s or `<percentage>`s
Animation type	a length, percentage or calc();

Formal syntax

border-top-left-radius = 
  <length-percentage [0,∞]>{1,2}  

<length-percentage> = 
  <length>      |
  <percentage>

Examples

Arc of a circle

A single <length> value produces an arc of a circle.

div {
  border-top-left-radius: 40px;
  background-color: lightgreen;
  border: solid 1px black;
  width: 100px;
  height: 100px;
}

Arc of an ellipse

Two different <length> values produce an arc of an ellipse.

div {
  border-top-left-radius: 40px 20px;
  background-color: lightgreen;
  border: solid 1px black;
  width: 100px;
  height: 100px;
}

Square element with percentage radius

A square element with a single <percentage> value produces an arc of a circle.

div {
  border-top-left-radius: 40%;
  background-color: lightgreen;
  border: solid 1px black;
  width: 100px;
  height: 100px;
}

Non-square element with percentage radius

A non-square element with a single <percentage> value produces an arc of an ellipse.

div {
  border-top-left-radius: 40%;
  background-color: lightgreen;
  border: solid 1px black;
  width: 200px;
  height: 100px;
}

Specifications

Specification
CSS Backgrounds and Borders Module Level 3 # the-border-radius

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`border-top-left-radius`	41	1212	49 4 Before Firefox 50, border styles of rounded corners were always rendered as if `border-style` was solid. This has been fixed in Firefox 50. 1–12	9	1510.5	53	≤37≤37	1818	49 4 Before Firefox 50, border styles of rounded corners were always rendered as if `border-style` was solid. This has been fixed in Firefox 50. 4–14	1411	4.21	1.01.0
`elliptical_corners`	1	12	3.5	9	10.5	3	≤37	18	4	14	1	1.0
`percentages`	4	12	4 1–4 Before Firefox 4, the `<percentage>` was relative to the width of the box even when specifying the radius for a height. This implied that `-moz-border-radius-bottomright` was always drawing an arc of circle, and never an ellipse, when followed by a single value.	9	10.5	5	≤37	18	4	14	4.2	1.0