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border-block-start-width CSS property

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since January 2020.

The border-block-start-width CSS property defines the width of the logical block-start border of an element, which maps to a physical border width depending on the element's writing mode, directionality, and text orientation. It corresponds to the border-top-width, border-right-width, border-bottom-width, or border-left-width property depending on the values defined for writing-mode, direction, and text-orientation.

In this article

Try it

border-block-start-width: thick;
writing-mode: horizontal-tb;

border-block-start-width: thick;
writing-mode: vertical-rl;

border-block-start-width: 4px;
writing-mode: horizontal-tb;

border-block-start-width: 4px;
writing-mode: vertical-lr;

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box with a border around it.
  </div>
</section>

#example-element {
  background-color: palegreen;
  color: black;
  border: 0 solid crimson;
  padding: 0.75em;
  width: 80%;
  height: 100px;
  unicode-bidi: bidi-override;
}

Syntax

css
/* <'line-width'> values */
border-block-start-width: 5px;
border-block-start-width: thick;

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

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

Values

<line-width>

Defines the width of the border, either as an explicit non-negative <length> or the keywords: thin, medium, or thick. The default is medium.

Formal definition

Initial valuemedium
Applies toall elements
Inheritedno
Computed valuethe absolute <length>, snapped as a line width
Animation typeby computed value type

Formal syntax

border-block-start-width = 
  <line-width>  

<line-width> = 
  <length [0,]>  |
  hairline        |
  thin            |
  medium          |
  thick
This syntax reflects the latest standard as per CSS Borders and Box Decorations Module Level 4. Not all browsers may have implemented every part. See Browser compatibility for support information.

Examples

Border width with vertical text

HTML

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

CSS

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

.exampleText {
  writing-mode: vertical-lr;
  border: 1px solid blue;
  border-block-start-width: 5px;
}

Results

Specifications

Specification
CSS Logical Properties and Values Module Level 1
# border-width

Browser compatibility

See also

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      4. stroke-linejoin
      5. stroke-miterlimit
      6. stroke-opacity
      7. stroke-width
    149. stroke
    150. tab-size
    151. table-layout
    152. text-*
      1. text-align
      2. text-align-last
      3. text-anchor
      4. text-autospace
      5. text-box
      6. text-box-edge
      7. text-box-trim
      8. text-combine-upright
      9. text-decoration
      10. text-decoration-color
      11. text-decoration-inset
      12. text-decoration-line
      13. text-decoration-skip
      14. text-decoration-skip-ink
      15. text-decoration-style
      16. text-decoration-thickness
      17. text-emphasis
      18. text-emphasis-color
      19. text-emphasis-position
      20. text-emphasis-style
      21. text-indent
      22. text-justify
      23. text-orientation
      24. text-overflow
      25. text-rendering
      26. text-shadow
      27. text-size-adjust
      28. text-spacing-trim
      29. text-transform
      30. text-underline-offset
      31. text-underline-position
      32. text-wrap
      33. text-wrap-mode
      34. text-wrap-style
    153. timeline-scope
    154. top
    155. touch-action
    156. transform-*
      1. transform-box
      2. transform-origin
      3. transform-style
    157. transform
    158. transition-*
      1. transition-behavior
      2. transition-delay
      3. transition-duration
      4. transition-property
      5. transition-timing-function
    159. transition
    160. translate
    161. unicode-bidi
    162. user-modify
    163. user-select
    164. vector-effect
    165. vertical-align
    166. view-*
      1. view-timeline
      2. view-timeline-axis
      3. view-timeline-inset
      4. view-timeline-name
      5. view-transition-class
      6. view-transition-name
      7. view-transition-scope
    167. visibility
    168. white-space
    169. white-space-collapse
    170. widows
    171. width
    172. will-change
    173. word-break
    174. word-spacing
    175. writing-mode
    176. x
    177. y
    178. z-index
    179. zoom
  53. Selectors
    1. & nesting selector
    2. Attribute selectors
    3. Class selectors
    4. ID selectors
    5. Keyframe selectors
    6. Namespace separator
    7. Selector list
    8. Type selectors
    9. Universal selectors
  54. Combinators
    1. Child combinator
    2. Column combinator
    3. Descendant combinator
    4. Next-sibling combinator
    5. Subsequent-sibling combinator
  55. Pseudo-classes
    1. :-moz-*
      1. :-moz-broken
      2. :-moz-drag-over
      3. :-moz-first-node
      4. :-moz-handler-blocked
      5. :-moz-handler-crashed
      6. :-moz-handler-disabled
      7. :-moz-last-node
      8. :-moz-loading
      9. :-moz-locale-dir(ltr)
      10. :-moz-locale-dir(rtl)
      11. :-moz-only-whitespace
      12. :-moz-submit-invalid
      13. :-moz-suppressed
      14. :-moz-user-disabled
      15. :-moz-window-inactive
    2. :active-view-transition
    3. :active-view-transition-type()
    4. :active
    5. :any-link
    6. :autofill
    7. :blank
    8. :buffering
    9. :checked
    10. :current
    11. :default
    12. :defined
    13. :dir()
    14. :disabled
    15. :empty
    16. :enabled
    17. :first-child
    18. :first-of-type
    19. :first
    20. :focus-visible
    21. :focus-within
    22. :focus
    23. :fullscreen
    24. :future
    25. :has-slotted
    26. :has()
    27. :heading
    28. :heading()
    29. :host-context()
    30. :host
    31. :host()
    32. :hover
    33. :in-range
    34. :indeterminate
    35. :interest-source
    36. :interest-target
    37. :invalid
    38. :is()
    39. :lang()
    40. :last-child
    41. :last-of-type
    42. :left
    43. :link
    44. :local-link
    45. :modal
    46. :muted
    47. :not()
    48. :nth-*
      1. :nth-child()
      2. :nth-last-child()
      3. :nth-last-of-type()
      4. :nth-of-type()
    49. :only-child
    50. :only-of-type
    51. :open
    52. :optional
    53. :out-of-range
    54. :past
    55. :paused
    56. :picture-in-picture
    57. :placeholder-shown
    58. :playing
    59. :popover-open
    60. :read-only
    61. :read-write
    62. :required
    63. :right
    64. :root
    65. :scope
    66. :seeking
    67. :stalled
    68. :state()
    69. :target-*
      1. :target-after
      2. :target-before
      3. :target-current
    70. :target
    71. :user-invalid
    72. :user-valid
    73. :valid
    74. :visited
    75. :volume-locked
    76. :where()
    77. :xr-overlay
  56. Pseudo-elements
    1. ::-moz-*
      1. ::-moz-color-swatch
      2. ::-moz-focus-inner
      3. ::-moz-list-bullet
      4. ::-moz-list-number
      5. ::-moz-meter-bar
      6. ::-moz-progress-bar
      7. ::-moz-range-progress
      8. ::-moz-range-thumb
      9. ::-moz-range-track
    2. ::-webkit-*
      1. ::-webkit-inner-spin-button
      2. ::-webkit-meter-bar
      3. ::-webkit-meter-even-less-good-value
      4. ::-webkit-meter-inner-element
      5. ::-webkit-meter-optimum-value
      6. ::-webkit-meter-suboptimum-value
      7. ::-webkit-progress-bar
      8. ::-webkit-progress-inner-element
      9. ::-webkit-progress-value
      10. ::-webkit-scrollbar
      11. ::-webkit-search-cancel-button
      12. ::-webkit-search-results-button
      13. ::-webkit-slider-runnable-track
      14. ::-webkit-slider-thumb
    3. ::after
    4. ::backdrop
    5. ::before
    6. ::checkmark
    7. ::column
    8. ::cue
    9. ::details-content
    10. ::file-selector-button
    11. ::first-letter
    12. ::first-line
    13. ::grammar-error
    14. ::highlight()
    15. ::marker
    16. ::part()
    17. ::picker-icon
    18. ::picker()
    19. ::placeholder
    20. ::scroll-*
      1. ::scroll-button()
      2. ::scroll-marker
      3. ::scroll-marker-group
    21. ::search-text
    22. ::selection
    23. ::slotted()
    24. ::spelling-error
    25. ::target-text
    26. ::view-*
      1. ::view-transition
      2. ::view-transition-group()
      3. ::view-transition-image-pair()
      4. ::view-transition-new()
      5. ::view-transition-old()
  57. At-rules
    1. @charset
    2. @color-profile
    3. @container
    4. @counter-style
      1. additive-symbols
      2. fallback
      3. negative
      4. pad
      5. prefix
      6. range
      7. speak-as
      8. suffix
      9. symbols
      10. system
    5. @custom-media
    6. @document
    7. @font-face
      1. ascent-override
      2. descent-override
      3. font-display
      4. font-family
      5. font-feature-settings
      6. font-stretch
      7. font-style
      8. font-variation-settings
      9. font-weight
      10. font-width
      11. line-gap-override
      12. size-adjust
      13. src
      14. unicode-range
    8. @font-feature-values
      1. font-display
    9. @font-palette-values
      1. base-palette
      2. font-family
      3. override-colors
    10. @function
    11. @import
    12. @keyframes
    13. @layer
    14. @media
      1. -moz-device-pixel-ratio
      2. -webkit-animation
      3. -webkit-device-pixel-ratio
      4. -webkit-transform-2d
      5. -webkit-transform-3d
      6. -webkit-transition
      7. any-hover
      8. any-pointer
      9. aspect-ratio
      10. color
      11. color-gamut
      12. color-index
      13. device-aspect-ratio
      14. device-height
      15. device-posture
      16. device-width
      17. display-mode
      18. dynamic-range
      19. forced-colors
      20. grid
      21. height
      22. horizontal-viewport-segments
      23. hover
      24. inverted-colors
      25. monochrome
      26. orientation
      27. overflow-block
      28. overflow-inline
      29. pointer
      30. prefers-color-scheme
      31. prefers-contrast
      32. prefers-reduced-data
      33. prefers-reduced-motion
      34. prefers-reduced-transparency
      35. resolution
      36. scan
      37. scripting
      38. shape
      39. update
      40. vertical-viewport-segments
      41. video-dynamic-range
      42. width
    15. @namespace
    16. @page
      1. page-orientation
      2. size
    17. @position-try
    18. @property
      1. inherits
      2. initial-value
      3. syntax
    19. @scope
    20. @starting-style
    21. @supports
    22. @view-transition
  58. Values
    1. !important
    2. fit-content
    3. inherit
    4. initial
    5. max-content
    6. min-content
    7. revert
    8. revert-layer
    9. revert-rule
    10. unset
  59. Types
    1. <absolute-size>
    2. <alpha-value>
    3. <angle-percentage>
    4. <angle>
    5. <axis>
    6. <baseline-position>
    7. <basic-shape>
    8. <blend-mode>
    9. <box-edge>
    10. <calc-keyword>
    11. <calc-sum>
    12. <color-interpolation-method>
    13. <color>
    14. <content-distribution>
    15. <content-position>
    16. <corner-shape-value>
    17. <custom-ident>
    18. <dashed-function>
    19. <dashed-ident>
    20. <dimension>
    21. <display-box>
    22. <display-inside>
    23. <display-internal>
    24. <display-legacy>
    25. <display-listitem>
    26. <display-outside>
    27. <easing-function>
    28. <filter-function>
    29. <flex>
    30. <frequency-percentage>
    31. <frequency>
    32. <generic-family>
    33. <gradient>
    34. <hex-color>
    35. <hue-interpolation-method>
    36. <hue>
    37. <ident>
    38. <image>
    39. <integer>
    40. <length-percentage>
    41. <length>
    42. <line-style>
    43. <line-width>
    44. <named-color>
    45. <number>
    46. <overflow-position>
    47. <overflow>
    48. <percentage>
    49. <position-area>
    50. <position>
    51. <ratio>
    52. <relative-size>
    53. <resolution>
    54. <rule-list>
    55. <self-position>
    56. <shape>
    57. <string>
    58. <system-color>
    59. <text-edge>
    60. <time-percentage>
    61. <time>
    62. <timeline-range-name>
    63. <transform-function>
    64. <url>
  60. Functions
    1. -moz-image-rect()
    2. abs()
    3. acos()
    4. alpha()
    5. anchor-size()
    6. anchor()
    7. asin()
    8. atan()
    9. atan2()
    10. attr()
    11. blur()
    12. brightness()
    13. calc-size()
    14. calc()
    15. circle()
    16. clamp()
    17. color-mix()
    18. color()
    19. conic-gradient()
    20. contrast-color()
    21. contrast()
    22. cos()
    23. counter()
    24. counters()
    25. cross-fade()
    26. cubic-bezier()
    27. device-cmyk()
    28. drop-shadow()
    29. dynamic-range-limit-mix()
    30. element()
    31. ellipse()
    32. env()
    33. exp()
    34. fit-content()
    35. grayscale()
    36. hsl()
    37. hue-rotate()
    38. hwb()
    39. hypot()
    40. if()
    41. image-set()
    42. image()
    43. inset()
    44. invert()
    45. lab()
    46. lch()
    47. light-dark()
    48. linear-gradient()
    49. linear()
    50. log()
    51. matrix()
    52. matrix3d()
    53. max()
    54. min()
    55. minmax()
    56. mod()
    57. oklab()
    58. oklch()
    59. opacity()
    60. paint()
    61. param()
    62. path()
    63. perspective()
    64. polygon()
    65. pow()
    66. progress()
    67. radial-gradient()
    68. random()
    69. ray()
    70. rect()
    71. rem()
    72. repeat()
    73. repeating-conic-gradient()
    74. repeating-linear-gradient()
    75. repeating-radial-gradient()
    76. rgb()
    77. rotate()
    78. rotate3d()
    79. rotateX()
    80. rotateY()
    81. rotateZ()
    82. round()
    83. saturate()
    84. scale()
    85. scale3d()
    86. scaleX()
    87. scaleY()
    88. scaleZ()
    89. sepia()
    90. shape()
    91. sibling-count()
    92. sibling-index()
    93. sign()
    94. sin()
    95. skew()
    96. skewX()
    97. skewY()
    98. sqrt()
    99. steps()
    100. superellipse()
    101. symbols()
    102. tan()
    103. translate()
    104. translate3d()
    105. translateX()
    106. translateY()
    107. translateZ()
    108. type()
    109. url()
    110. var()
    111. xywh()
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