CSS: “width”: X is not a “width” value.

The CSS width property contains an invalid value.

The width property accepts specific types of values: lengths (like 100px, 10em, 5rem), percentages (50%), viewport units (100vw), the keyword auto, and sizing keywords like max-content, min-content, or fit-content. The validator rejects anything that doesn't match these formats.

Common mistakes that trigger this error:

• Missing a unit: width: 100 instead of width: 100px. Plain numbers (other than 0) are not valid CSS lengths.
• Using an invalid unit or typo: width: 100 px (with a space), width: 100ppx.
• Passing a non-length value: width: red, width: bold, width: none. The keyword none works for max-width but not for width.
• Including extra characters: width: 100px;50px or width: 100px !importnt.

Invalid example

<div style="width: 600">
  <p>This box has no unit on its width value.</p>
</div>

The value 600 is not valid because it lacks a CSS unit.

Fixed example

<div style="width: 600px">
  <p>This box now has a valid width.</p>
</div>

Adding px (or another appropriate unit like em, %, rem, vw) makes the value valid. If the intent is to let the element size itself naturally, use width: auto instead.

Learn more:

MDN Reference

CSS width property - MDN Web Docs

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MDN Reference

CSS Values and Units - MDN Web Docs

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web.dev Article

Learn CSS: Sizing - web.dev

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