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.

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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.


/* <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: revert;
border-start-start-radius: revert-layer;
border-start-start-radius: unset;



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 value0
Applies toall 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.
Percentagesrefer to the corresponding dimension of the border box
Computed valuetwo absolute <length>s or <percentage>s
Animation typea length, percentage or calc();

Formal syntax

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

<length-percentage> =
<length> |


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;



CSS Logical Properties and Values Level 1
# border-radius-properties

Browser compatibility

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See also