 Una Kravets [X](https://twitter.com/una) [Mastodon](https://front-end.social/@una) [Homepage](https://una.im)
The CSS Anchor Positioning API lets you position elements relative to other elements, known as *anchors*. This API simplifies complex layout requirements for many interface features like menus and submenus, tooltips, selects, labels, cards, settings dialogs, and many more. With anchor positioning built into the browser, you can build layered user interfaces without relying on third-party libraries, opening a world of creative possibilities.
Browser Support
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[Source](https://developer.mozilla.org/docs/Web/CSS/Reference/Values/anchor)
## Core Concepts: Anchors and positioned elements
At the heart of this API lies the relationship between *anchors* and *positioned elements* . An anchor is an element designated as a reference point using the `anchor-name` property. A positioned element is an element placed relative to an anchor using the `position-anchor` property or explicitly using `anchor-name` in its positioning logic.
 Anchor elements and positioned elements.
## Set up anchors
Creating an anchor is straightforward. Apply the anchor-name property to the selected element, and assign it a unique identifier. This unique identifier must be prepended with a double dash, much like a CSS variable.
```css
.anchor-button {
anchor-name: --anchor-el;
}
```
Once assigned an anchor-name, `.anchor-button` serves as an anchor, ready to guide the placement of other elements. You can connect this anchor to other elements in one of two ways:
### Implicit anchors
The first way to connect an anchor to another element is with an *implicit anchor* as in the following code example. The `position-anchor` property is added to the element you want to connect to your anchor, and has the name of the anchor (in this case `--anchor-el`) as a value.
```css
.positioned-notice {
position-anchor: --anchor-el;
}
```
With an implicit anchor relationship, you can position elements using the `anchor()` function without explicitly specifying the anchor name at its first argument.
```css
.positioned-notice {
position-anchor: --anchor-el;
top: anchor(bottom);
}
```
### Explicit anchors
Alternatively, you can use the anchor name directly in the anchor function (for example, `top: anchor(--anchor-el bottom`). This is called an **explicit anchor**, and can be handy if you want to anchor to multiple elements (read on for an example).
```css
.positioned-notice {
top: anchor(--anchor-el bottom);
}
```
## Position elements relative to anchors
 Anchor positioning diagram with physical properties.
Anchor positioning builds on CSS absolute positioning To use positioning values you need to add `position: absolute` to your positioned element. Then, use the `anchor()` function to apply positioning values. For example, to position an anchored element at the top left of the anchoring element, use the following positioning:
```css
.positioned-notice {
position-anchor: --anchor-el;
/* absolutely position the positioned element */
position: absolute;
/* position the right of the positioned element at the right edge of the anchor */
right: anchor(right);
/* position the bottom of the positioned element at the top edge of the anchor */
bottom: anchor(top);
}
```
 Diagram of positioning edges on the positioned element.
Now you have one element anchored to another, like so:
Demo of a basic anchor.
To use logical positioning for these values, the equivalents are as follows:
- `top` = `inset-block-start`
- `left`= `inset-inline-start`
- `bottom` = `inset-block-end`
- `right`= `inset-inline-end`
### Center a positioned element with `anchor-center`
To make it easier to center your anchor positioned element relative to its anchor, there's a new value called `anchor-center` which can be used with the `justify-self`, `align-self`, `justify-items`, and `align-items` properties.
This example modifies the previous one by using `justify-self: anchor-center` to center the positioned element on top of its anchor.
```css
.positioned-notice {
position: absolute;
/* Anchor reference */
position-anchor: --anchor-el;
/* Position bottom of positioned elem at top of anchor */
bottom: anchor(top);
/* Center justification to the anchor */
justify-self: anchor-center;
}
```
Demo of an anchor centered using `justify-center`.
### Multiple anchors
Elements can be tethered to more than one anchor. This means you may need to set position values that are positioned relative to more than one anchor. Do this by using the `anchor()` function and explicitly stating which anchor you are referencing in the first argument. In the following example, the top-left of a positioned element is anchored to the bottom-right of one anchor, and the bottom-right of the positioned element is anchored to the top-left of the second anchor:
```css
.anchored {
position: absolute;
top: anchor(--one bottom);
left: anchor(--one right);
right: anchor(--two left);
bottom: anchor(--two top);
}
```
Demo showing multiple anchors.
## Position with `position-area`
The anchoring API includes a new layout mechanism using the `position-area` property.
This property lets you place anchor positioned elements relative to their respective anchors, and works on a 9-cell grid with the anchoring element in the center.
To use `position-area` rather than absolute positioning, use the `position-area` property, with physical or logical values. For example:
- Top-center: `position-area: top` or `position-area: block-start`
- Left-center: `position-area: left` or `position-area: inline-start`
- Bottom-center: `position-area: bottom` or `position-area: block-end`
- Right-center: `position-area: right` or `position-area: inline-end`
Demo showing multiple anchors.
To explore these positions further, check out the following tool:
Anchor tool for position-area positions.
## Size elements with `anchor-size()`
The `anchor-size()` function, also part of the anchor positioning API, can be used to size or position an anchor positioned element based on the size of its anchor (width, height, or inline and block sizes).
The following CSS shows an example of using this for height,using `anchor-size(height)` within a `calc()` function to set the maximum height of the tooltip to be two times the height of the anchor.
```css
.positioned-notice {
position-anchor: --question-mark;
/* set max height of the tooltip to 2x height of the anchor */
max-height: calc(anchor-size(height) * 2);
}
```
Demo for `anchor-size`
## Use anchor with top-layer elements like popover and dialog
Anchor positioning works incredibly well with top-layer elements like [`popover`](https://web.dev/blog/popover-api). and `