The border-start-start-radius CSS property defines a logical border radius on an element, which maps to a physical border radius that depends on the element's writing-mode, direction, and text-orientation. This is useful when building styles to work regardless of the text orientation and writing mode.

/* <length> values */
/* With one value the corner will be a circle */
border-start-start-radius: 10px;  
border-start-start-radius: 1em;   

/* With two values the corner will be an ellipse */
border-start-start-radius: 1em 2em;

/* Global values */
border-start-start-radius: inherit;
border-start-start-radius: initial;
border-start-start-radius: unset;

This property affects the corner between the block-start and the inline-start sides of the element. For instance, in a horizontal-tb writing mode with ltr direction, it corresponds to the border-top-left-radius property.



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


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


Border radius with vertical text


  <p class="exampleText">Example</p>


div {
  background-color: rebeccapurple;
  width: 120px;
  height: 120px;
  border-start-start-radius: 10px;

.exampleText {
  writing-mode: vertical-rl;
  padding: 10px;
  background-color: #fff;
  border-start-start-radius: 10px;



Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
border-start-start-radius No No 66 No No No
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
border-start-start-radius No No 66 No No No

See also

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