Logical properties for floating and positioning

The table below details the logical properties and values discussed in this guide along with their physical properties and values mappings. They assume a horizontal writing-mode, with a left-to-right direction.

In addition to these mapped properties, there are some additional shorthand properties made possible by being able to address block and inline dimensions. These have no mapping to physical properties, aside from the inset property.

The physical values used with the float and clear properties are left, right and both. The CSS logical properties and values module defines the values inline-start and inline-end as mappings for left and right.

In the example below, the first box is floated with float: left, and the second with float: inline-start. If you apply direction: rtl to the .inner selector, the left-floated box always stays on the left, whereas the inline-start-floated item follows the direction of the text. You can combine this with writing-mode: vertical-rl to see the difference of block layout in combination with direction values.

<div class="container">
  <div class="inner">
    <div class="physical box"></div>
    Turnip greens yarrow ricebean rutabaga endive cauliflower sea lettuce
    kohlrabi amaranth water spinach avocado daikon napa cabbage asparagus winter
    purslane kale.
  </div>
  <div class="inner">
    <div class="logical box"></div>
    Turnip greens yarrow ricebean rutabaga endive cauliflower sea lettuce
    kohlrabi amaranth water spinach avocado daikon napa cabbage asparagus winter
    purslane kale.
  </div>
</div>

body {
  font: 1.2em / 1.5 sans-serif;
}
.container {
  display: flex;
}

.box {
  border: 2px solid rgb(96 139 168);
  border-radius: 5px;
  background-color: rgb(96 139 168 / 0.2);
  padding: 10px;
  margin: 10px;
  width: 100px;
  height: 100px;
}

.inner {
  /* direction: rtl; */
  /* writing-mode: vertical-rl; */
}

.physical {
  float: left;
}

.logical {
  float: inline-start;
}

CSS positioning generally allows us to position an element in a manner relative to its containing block — we essentially inset the item relative to where it would fall based on normal flow. To position an element relative to the viewport, use the physical properties top, right, bottom and left. When you want the positioning to relate to the flow of text in your writing mode, use inset-block-start, inset-block-end, inset-inline-start and inset-inline-end instead.

These properties take a length or a percentage as a value, and relate to the user's screen dimensions.

In the below example, the inset-block-start and inset-inline-end properties are used to position the blue box using absolute positioning inside the area with the grey dotted border, which has position: relative. Change the writing-mode property to vertical-rl, or add direction: rtl, and see how the flow relative box stays with the text direction.

<div class="container">
  <div class="inner">
    <div class="physical box"></div>
  </div>
  <div class="inner">
    <div class="logical box"></div>
  </div>
</div>

.container {
  display: flex;
}

.inner {
  width: 200px;
  height: 200px;
  position: relative;
  border: 2px dotted grey;
}

.box {
  border: 2px solid rgb(96 139 168);
  border-radius: 5px;
  background-color: rgb(96 139 168 / 0.2);
  padding: 10px;
  width: 100px;
  height: 100px;
}

.inner {
  writing-mode: horizontal-tb;
}

.physical {
  position: absolute;
  top: 20px;
  right: 0;
}

.logical {
  position: absolute;
  inset-block-start: 20px;
  inset-inline-end: 0;
}

As with other properties in the module, we have shorthand properties which give the ability to set two or four values at once.

• inset — sets all four sides together with physical mapping.
• inset-inline — sets both logical inline insets.
• inset-block — sets both logical block insets.

The text-align property has logical values that relate to text direction — rather than using left and right you can use start and end. In the below example, text-align: right is set in the first block and text-align: end in the second.

If you change the value of direction to rtl, you will see that the alignment stays to the right for the first block, but goes to the logical end on the left in the second.

<div class="container">
  <div class="inner physical">Aligned text</div>
  <div class="inner logical">Aligned text</div>
</div>

body {
  font: 1.2em / 1.5 sans-serif;
}

.container {
  display: flex;
}

.inner {
  width: 200px;
  border: 2px dotted grey;
  padding: 10px;
}

.inner {
  direction: ltr;
}

.physical {
  text-align: right;
}

.logical {
  text-align: end;
}

This works more consistently when using box alignment that uses start and end rather than physical directions for alignment.