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Form controls must appear sufficiently distinct from their surroundings, so that people 
with visual impairments are still able to clearly see them.    

Either the border or the form control itself must have a 3:1 colour contrast with the 
surrounding area. 

## Methodology

* All `<input>`, `<textarea>`, and `<select>` elements are checked.
* For `<input>` elements, these types are ignored as their
  appearance is controlled by the browser or operating system:
  `checkbox`, `radio`, `submit`, `reset`, `image`, `hidden`, `file`. 
* The flattened background color of the control is determined. This is the color of the
  control itself, combined with any parent elements if the control is transparent.
* If the control has a border or outline:
  * The flattened background color of each edge is determined. 
    This is the color of the edge itself, combined with any parent elements
    if the edge is transparent.
  * If any edge has sufficient contrast with the flattened background color of the control, 
    the control is considered to have sufficient contrast.
* If the control does not have a border or outline:
  * The flattened background color of the surrounding 
    area is determined. This is the color of the first control's parent element which is at least 
    one pixel larger around the element in every dimension, i.e. above, below, left, and right.
  * If the background color of the element has sufficient contrast with surrounding area color
    the control is considered to have sufficient contrast.

## Troubleshooting

There are some limitations to the contrast checker:

* The use of drop shadows, glowing effects, gradients, and other complex effects 
  mean there is no one clear color to determine the contrast ratio against. 
  In these cases, the contrast ratio cannot currently be determined.
* It is possible for an element to be positioned over multiple elements, e.g. via
  `position: absolute` or `position: fixed`. In this case, the contrast ratio cannot 
  currently be determined.

## Further reading

* [WCAG 1.4.11](https://www.w3.org/WAI/WCAG21/Understanding/non-text-contrast.html)

non-text-contrast

January 2025

December 2024

The National Archives

Title / URL	Issues
Cookies - Legalwww.nationalarchives.gov.uk/legal/cookies/	5
Online exhibitions Archive - The National Archiveswww.nationalarchives.gov.uk/online-exhibitions/	4
Research guides - The National Archiveswww.nationalarchives.gov.uk/help-with-your-research/research-guides/	2
PRONOM \| Welcomewww.nationalarchives.gov.uk/PRONOM/	2
Record copying - The National Archiveswww.nationalarchives.gov.uk/help-with-your-research/record-copying/	1
Student and work placements - The National Archiveswww.nationalarchives.gov.uk/about/jobs/student-and-work-placements/	1
Accessibility statement - Website help and terms of usewww.nationalarchives.gov.uk/help/web-accessibility/	1
News - The National Archiveswww.nationalarchives.gov.uk/about/news/?news-tag=funding&news-view=child?news-tag=funding&news-view=child	1
News - The National Archiveswww.nationalarchives.gov.uk/about/news/page/2/	1
Visit us - The National Archiveswww.nationalarchives.gov.uk/about/visit-us/	1

Ensure form controls contrast sufficiently with their surroundings

The National Archives

Where this issue has occurred