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border-top-left-radius

The border-top-left-radius CSS property sets the rounding of the top-left corner of the element.

/* 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;

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.

border-radius.png

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.

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.
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
Media visual
Computed value two absolute <length>s or <percentage>s
Animation type a length, percentage or calc();
Canonical order the unique non-ambiguous order defined by the formal grammar

Syntax

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 syntax

<length-percentage>{1,2}
where 
<length-percentage> = <length> | <percentage>

Examples

Live example Code
An arc of ellipse is used as the border 
div {
  border-top-left-radius: 40px 40px;
}
An arc of ellipse is used as the border 
div {
  border-top-left-radius: 40px 20px;
}
The box is a square: an arc of circle is used as the border 
div {
  border-top-left-radius: 40%;
}
The box is not a square: an arc of ellipse is used as the border 
div {
  border-top-left-radius: 40%;
}
The background color is clipped at the border 
div {
  border-top-left-radius:40%;
  border-style: black 3px double;
  background-color: rgb(250,20,70);
  background-clip: content-box;
}

Specifications

Specification Status Comment
CSS Backgrounds and Borders Module Level 3
The definition of 'border-top-left-radius' in that specification.		 Candidate Recommendation Initial definition

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari
Basic support

4

1 -webkit-

Yes

Yes -webkit-

41

49 -webkit-

44 -webkit- 2

1 — 123

 9 10.5

5

3 -webkit-

Percentages 4 Yes

4

14

 9 10.5 5
Ellipitcal corners 1 Yes 3.5 9 10.5 3
Feature Android webview Chrome for Android Edge mobile Firefox for Android IE mobile Opera Android iOS Safari
Basic support ? ?

Yes

Yes -webkit-

Yes1 ? ? ?
Percentages ? ? Yes Yes ? ? ?
Ellipitcal corners ? ? Yes Yes ? ? ?

1. Prior to Firefox 50, border styles of rounded corners were always rendered as if border-style was solid. This has been fixed in Firefox 50.

2. From version 44: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.

3. Supported as -moz-border-radius-topright.

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-topright was always drawing an arc of circle, and never an ellipse, when followed by a single value.

See also

The border-radius-related CSS properties: the CSS shorthand border-radius, the properties for the other corners: border-top-right-radius, border-bottom-right-radius, and border-bottom-left-radius.

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https://developer.mozilla.org/en-US/docs/Web/CSS/border-top-left-radius