The following values may be specified for an element.

none

The element has no intrinsic width.

<length>

The element has the specified width (<length>).

auto <length>

A remembered value of the "normally rendered" element width if one exists and the element is skipping its contents (for example, when it is offscreen); otherwise the specified <length>.

The property is commonly applied alongside elements that can trigger size containment, such as contain: size and content-visibility, and may also be set using the contain-intrinsic-size shorthand property.

Size containment allows a user agent to layout an element as though it had a fixed size, preventing unnecessary reflows by avoiding the re-rendering of child elements to determine the actual size (thereby improving user experience). By default, size containment treats elements as though they had no contents, and may collapse the layout in the same way as if the contents had no width or height. The contain-intrinsic-width property allows authors to specify an appropriate value to be used as the width for layout.

The auto <length> value allows the width of the element to be stored if the element is ever "normally rendered" (with its child elements), and then used instead of the specified width when the element is skipping its contents. This allows offscreen elements with content-visibility: auto to benefit from size containment without developers having to be as precise in their estimates of element size. The remembered value is not used if the child elements are being rendered (if size containment is enabled, the <length> will be used).

contain-intrinsic-width = 
  none           |
  <length>       |
  auto <length>  

In addition to the example below, the contain-intrinsic-size page contains a live example that demonstrates the effect of modifying the intrinsic width and height.

The HTML below defines an element "contained_element" that will be subject to size constraint, and which contains a child element.

<div id="contained_element">
  <div class="child_element"></div>
</div>

The CSS below sets the content-visibility of contained_element to auto, so if the element is hidden it will be size constrained. The width and height that are used when it is size constrained are set at the same time using contain-intrinsic-width and contain-intrinsic-height, respectively.

#contained_element {
  border: 2px solid green;
  width: 151px;
  content-visibility: auto;
  contain-intrinsic-width: 152px;
  contain-intrinsic-height: 52px;
}
.child_element {
  border: 1px solid red;
  background: blue;
  height: 50px;
  width: 150px;
}

• content-visibility: the new CSS property that boosts your rendering performance (web.dev)
• contain-intrinsic-size
• contain-intrinsic-height
• contain-intrinsic-block-size
• contain-intrinsic-inline-size