CSS - inset-block-start

The CSS property inset-block-start determines the logical block start offset of an element. It depends upon the writing mode, direction and text orientation of the element. It relates to the top and bottom, or left and right CSS properties.

Possible Values

The CSS property inset-block-start takes the same set of values as left CSS property, which are as follows:

  • <length> − Can specify a negative, null or positive value.

  • <percentage> − Percentage of the container's width.

  • auto − Default value. Browser calculates the left position.

  • inherit − Specifies the same value as computed from its parent element.

Applies To

All positioned elements.

Syntax

inset-block-start = auto | <length-percentage> 

/* <length> values */
inset-block-start: 5px;
inset-block-start: 3.4em;
   
/* <percentage>s of the width or height of the containing block */
inset-block-start: 15%;
   
/* Keyword value */
inset-block-start: auto;

CSS inset-block-start - Setting Offset

The following example demonstrates the use of inset-block-start property with a length value passed to it, which determines the start offset value.

<html>
<head>
<style>
   div {
      background-color: darkslategrey;
      width: 180px;
      height: 120px;
      position: relative;
   }

   .inset-ex {
      writing-mode: horizontal-tb;
      position: absolute;
      inset-block-start: 50px;
      background-color: white;
   }
</style>
</head>
<body>
   <div>
      <span class="inset-ex">inset-block-start</span>
   </div>
</body>
</html>

CSS inset-block-start - Percentage Value

The following example demonstrates the use of inset-block-start property with a percentage value passed to it, which determines the start offset value. The writing mode is set as horizontal-tb.

<html>
<head>
<style>
   div {
      background-color: darkslategrey;
      width: 180px;
      height: 120px;
      position: relative;
   }

   .inset-ex {
      writing-mode: horizontal-tb;
      position: absolute;
      inset-block-start: 50%;
      background-color: white;
   }
</style>
</head>
<body>
   <div>
      <span class="inset-ex">inset-block-start</span>
   </div>
</body>
</html>

CSS inset-block-start - With direction

The following example demonstrates the use of inset-block-start property with writing-mode as vertical-lr and direction as rtl.

<html>
<head>
<style>
   div {
      background-color: darkslategrey;
      width: 180px;
      height: 120px;
      position: relative;
   }

   .inset-ex {
      writing-mode: vertical-lr;
      direction: rtl;
      position: absolute;
      inset-block-start: 150px;
      background-color: white;
   }
</style>
</head>
<body>
   <div>
      <span class="inset-ex">inset-block-start</span>
   </div>
</body>
</html>

CSS inset-block-start - auto Value

The following example demonstrates the use of inset-block-start property with auto as value passed to it, which determines the start offset value. The writing mode is also set as horizontal-tb.

<html>
<head>
<style>
   div {
      background-color: darkslategrey;
      width: 180px;
      height: 120px;
      position: relative;
   }

   .inset-ex {
      writing-mode: horizontal-tb;
      position: absolute;
      inset-block-start: auto;
      background-color: white;
   }
</style>
</head>
<body>
   <div>
      <span class="inset-ex">inset-block-start</span>
   </div>
</body>
</html>
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