This property is a shorthand for the following CSS properties:

• border-block-start-color
• border-block-start-style
• border-block-start-width

border-block-start: 1px;
border-block-start: 2px dotted;
border-block-start: medium dashed blue;

/* Global values */
border-block-start: inherit;
border-block-start: initial;
border-block-start: revert;
border-block-start: revert-layer;
border-block-start: unset;

border-block-start can be used to set the values for one or more of border-block-start-width, border-block-start-style, and border-block-start-color. The physical border to which it maps depends on the element's writing mode, directionality, and text orientation. It corresponds to the border-top, border-right, border-bottom, or border-left property depending on the values defined for writing-mode, direction, and text-orientation.

Related properties are border-block-end, border-inline-start, and border-inline-end, which define the other borders of the element.

The border-block-start is specified with one or more of the following, in any order:

<'border-width'>

The width of the border. See border-width.

<'border-style'>

The line style of the border. See border-style.

<color>

The color of the border.

border-block-start = 
  <'border-top-width'>  ||
  <'border-top-style'>  ||
  <color>               

HTML

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

CSS

div {
  background-color: yellow;
  width: 120px;
  height: 120px;
}

.exampleText {
  writing-mode: vertical-rl;
  border-block-start: 5px dashed blue;
}

• CSS Logical Properties and Values
• This property maps to one of the physical border properties: border-top, border-right, border-bottom, or border-left.
• writing-mode, direction, text-orientation