border-block

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border-block is a CSS logical shorthand property that combines border-block-color, border-block-style, and border-block-width into a single declaration.

.element {
  border-block: 5px solid red;
  writing-mode: horizontal-tb;
}

border-block is the logical equivalent to physical properties including border-top and border-bottom (or border-right and border-left, depending on the writing-mode). It is defined in the CSS Logical Properties and Values Level 1 specification which is in Editor’s Draft at the time of this writing. The property is also the companion to border-inline, which styles borders that flow in the inline direction.

Two light gray boxes, side-by-side-. One has a solid orange border on the top and bottom. The one of the right has the same borders, but on the left and right. The left box is in a horizontal writing mode and the right box is in a vertical writing mode.
border-block styles the borders in the block direction, top and bottom, of an element by default, but it adapts to borders in the inline direction, left and right, when switching the writing-mode.

The writing-mode defaults to horizontal top-to-bottom if it is not explicitly declared.

The writing mode sets the direction

The direction of the borders depends on the writing-mode property. When the writing mode is set to the default horizontal direction, border-block is applied to the top and bottom borders of an element. Conversely, a vertical writing-mode, applies border-block to the right and left borders.

Syntax

The border-block logical property is a shorthand for setting both the start and end border-block-width, border-block-style and border-block-color in a single declaration. Again, the direction of “start” and “end” depends on the elements writing mode.

border-block: <border-block-width> || <border-block-style> || <border-block-color>

Browser support

IEEdgeFirefoxChromeSafariOpera
No92 166+87+14.1+73+
iOS
Safari
Android ChromeAndroid FirefoxAndroid BrowserOpera Mobile
14.7+92+90+92+64 1
Source: caniuse

1 Can be enabled by setting #enable-experimental-web-platform-features to enabled.

Constituent properties

Let’s look specifically at the border-block-width, border-block-style and border-block-color — the three properties that make up the border-block shorthand.

border-block-width

border-block-width is pretty much what you’d expect to get from the border-width property: it defines the thickness of the logical block borders of an element. The big difference being that border-block-width adapts to the element’s writing mode.

/* <'border-block-width'> values */
border-block-width: 15px;
border-block-width: thin; /* equivalent to 1px */
border-block-width: medium; /* equivalent to 3px */
border-block-width: thick; /* equivalent to 5px */

/* Global values */
border-block-width: inherit;
border-block-width: initial;
border-block-width: revert;
border-block-width: unset;
  • Initial: medium
  • Applies to: Same as border-top-width
  • Inherited: no
  • Percentages: n/a
  • Computed value: Same as corresponding border-*-width properties
  • Canonical order: per grammar
  • Animation type: discrete

border-block-width is also considered a shorthand property even though it is a constituent of border-block. It includes the following properties to control the widths of each individual border in the start and end direction of an element:

  • border-block-start-width: The width of the top border in a horizontal writing mode, the left border in a vertical left-to-right writing mode, and the right border in a vertical right-to-left writing mode.
  • border-block-end-width: The width of the bottom border in a horizontal writing mode, the right border in a vertical left-to-right writing mode, and the left border in a vertical right-to-left writing mode.
IEEdgeFirefoxChromeSafariOpera
No92 166+87+14.1+73+
iOS
Safari
Android ChromeAndroid FirefoxAndroid BrowserOpera Mobile
14.7+92+90+92+64 1
Source: caniuse

1 Can be enabled by setting #enable-experimental-web-platform-features to enabled.

border-block-style

border-block-style is the logical equivalent to border-style and is used exactly the same way to specify the type of line drawn around the element. In fact, it takes the exact same values as well.

/* <'border-block-style'> values */
border-block-style: hidden;
border-block-style: solid
border-block-style: dashed;
border-block-style: dotted;
border-block-style: double;
border-block-style: groove;
border-block-style: ridge;
border-block-style: inset;
border-block-style: outset;

/* Global values */
border-block-style: inherit;
border-block-style: initial;
border-block-style: revert;
border-block-style: unset;
  • Initial: none
  • Applies to: Same as border-top-style
  • Inherited: no
  • Percentages: n/a
  • Computed value: Same as corresponding border-*-style properties
  • Canonical order: per grammar
  • Animation type: discrete

border-block-style is also considered a shorthand property. It includes the following properties to control the type of line drawn for individual borders in the start and end direction of an element:

  • border-block-start-style: The style of the top border in a horizontal writing mode, the left border in a vertical left-to-right writing mode, and the right border in a vertical right-to-left writing mode.
  • border-block-end-style: The style of the bottom border in a horizontal writing mode, the right border in a vertical left-to-right writing mode, and the left border in a vertical right-to-left writing mode.
IEEdgeFirefoxChromeSafariOpera
No92 166+87+14.1+73+
iOS
Safari
Android ChromeAndroid FirefoxAndroid BrowserOpera Mobile
14.7+92+90+92+64 1
Source: caniuse

1 Can be enabled by setting #enable-experimental-web-platform-features to enabled.

border-block-color

border-block-color is used to specify the border color.

border-block-color: yellow;
border-block-color: #F5F6F7;
border-block-color: rgba(170, 50, 220, .6);
border-block-color: hsla(50, 100%, 50%, .6);

/* Global values */
border-block-color: inherit;
border-block-color: initial;
border-block-color: revert;
border-block-color: unset;
  • Initial: none
  • Applies to: Same as border-top-color
  • Inherited: no
  • Percentages: n/a
  • Computed value: Same as corresponding border-*-color properties
  • Canonical order: per grammar
  • Animation type: by computed value type

border-block-color is also considered a shorthand property. It includes the following properties to control the type of line drawn for individual borders in the start and end direction of an element:

  • border-block-start-color: The color of the top border in a horizontal writing mode, the left border in a vertical left-to-right writing mode, and the right border in a vertical right-to-left writing mode.
  • border-block-end-color: The color of the bottom border in a horizontal writing mode, the right border in a vertical left-to-right writing mode, and the left border in a vertical right-to-left writing mode.
IEEdgeFirefoxChromeSafariOpera
No79+41+69+12.1+56+
iOS
Safari
Android ChromeAndroid FirefoxAndroid BrowserOpera Mobile
12.2+92+90+92+64
Source: caniuse

Let’s talk about declaring just one side

But wait! You might be thinking of how you could just declare border for just one side of your container instead of having it top and bottom or left and right. If we were working with physical CSS properties, then we could simply reach for the individual border-top, border-bottom, border-right, and border-left properties.

But for Logical Properties, we make use of border-block-start, border-block-end, both of set individual borders. Let’s look specifically at both and see how they work.

border-block-start

border-block-start styles the logical “starting” border of an element. So, if we were working in, say, a default horizontal top-to-bottom writing mode, then the top border is the start and — spoiler alert — the bottom border is the end.

.box {
  border-block-start: 5px solid red;
  writing-mode: horizontal-tb;
  height: 200px;
  width: 200px;
}

But! If we were to change the writing direction to, say, vertical left-to-right, then the starting edge is rotated 90 degrees, which makes the left border the start.

And, if we switch things up to vertical right-to-left, you’ve can probably already guess it: the right border becomes the start.

Writing modeStarting border
horizontal-tbTop border
vertical-lrLeft border
vertical-rlRight border

border-block-end

border-block-end is everything we just looked at with border-block-start, only in the opposite direction. So, if the “start” in a horizontal top-to-bottom writing mode is the top border, the “end” is the bottom border.

.box {
  border-block-end: 5px solid red;
  writing-mode: horizontal-tb;
  height: 200px;
  width: 200px;
}
Writing modeEnding border
horizontal-tbBottom border
vertical-lrRight border
vertical-rlLeft border

Constituents to the constituents!

We just saw how border-block is shorthand for border-block-start and border-block-end. We also know that border-block takes three other properties as its values:

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

Well, if you can believe it, each of those properties are also shorthand for individual properties of their own. We can actually use these to style the width, style, and color of each individual border of an element by inserting “start” and “end” in the property name:

Start border propertiesWhat it does
border-block-start-widthSets the width of the “starting” border
border-block-start-styleSets the line style of the “starting” border
border-block-start-colorSets the color of the “starting” border
End border propertiesWhat it does
border-block-end-widthSets the width of the “ending” border
border-block-end-styleSets the line style of the “ending”border
border-block-end-colorSets the color of the “ending”border

More information

Further reading