概要

border-top-left-radius CSS プロパティは、要素の左上隅の丸め処理を設定します。丸めは、円または楕円とする事が可能です。 値を 0 とした場合の丸めは行われず、コーナーは正方形となります。

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.

背景、画像、色は、境界で丸くクリッピングされます。クリッピングの正確な場所は、background-clip プロパティの値によって定義されます。

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.

初期値0
適用対象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.
継承不可
相対値の基準refer to the corresponding dimension of the border box
メディアvisual
計算値絶対的な長さかパーセンテージ値の 2 値
アニメーションの可否可。 。両方の値が length の場合は、length 値として補完されます。両方の値が percentage の場合は、percentage 値として補完されます。それ以外の場合は、両方の値が calc() 関数にコンバートされ、length と percentage の合計になります (または各値が 0)。そして、これらの calc() 関数は、それぞれ半分ずつ補完された実数を持ちますの値として補完しますlength または percentage, calc();
正規順序形式文法で定義される一意のあいまいでない順序

構文

[ <length> | <percentage> ]{1,2}
border-top-left-radius: radius               /* the corner is a circle    */  E.g. border-top-left-radius: 3px
border-top-left-radius: horizontal vertical  /* the corner is an ellipsis */  E.g. border-top-left-radius: 0.5em 1em

border-top-left-radius: inherit

where:

radius
Is a <length> or a <percentage> denoting the radius of the circle to use for the border in that corner.
horizontal
Is a <length> or a <percentage> denoting the horizontal semi-major axis of the ellipsis to use for the border in that corner.
vertical
Is a <length> or a <percentage> denoting the vertical semi-major axis of the ellipsis to use for the border in that corner.

<length>
Denotes the size of the circle radius or the semi-major and semi-minor axes of the ellipsis. It can be expressed in any unit allowed by the CSS <length> data types. Negative values are invalid.
<percentage>
Denotes the size of the circle radius, or the semi-major and semi-minor axes of the ellipsis, using percentage values. Percentages for the horizontal axe refer to the width of the box, percentages for the vertical axe refer to the height of the box. Negative values are invalid.

Live example Code
 
An arc of circle 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;
}

仕様

仕様書 策定状況 コメント
CSS Backgrounds and Borders Module Level 3
border-top-left-radius の定義
勧告候補 Initial specification

ブラウザ実装状況

機能 Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
基本サポート 0.2 -webkit

1.0 (1.0) - 12.0 (12.0)-moz
但し後に仕様で定義された正式名称と異なる :
-moz-border-radius-topleft

9.0 10.5 3.0 (522) -webkit
4.0 4.0 (2.0) 5.0 (532.5)
相対値の指定 4.0 1.0 (1.0) with a bug (see note) 9.0 10.5 5.0 (532.5)
4.0 (2.0)
Elliptical corners 0.2 3.5 (1.9.1) 9.0 10.5 3.0 (522 )
機能 Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
基本サポート ? ? ? ? ?

ブラウザに関する注記

Gecko

  • The prefixed version (allowed from Firefox 1 to Firefox 12) of this property uses a different name, -moz-border-radius-topleft, than the final property as Mozilla implemented it before the final name was coined.
  • 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-topleft was always drawing an arc of circle, and never an ellipse, when followed by a single value.
  • Gecko is not able to display dotted and dashed rounded corners correctly: it displays them as solid (バグ 382721).

関連情報

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.

ドキュメントのタグと貢献者

 このページの貢献者: Simplexible, Sebastianz, Prinz_Rana, ethertank, FredB, Yuichiro
 最終更新者: Simplexible,