Sign up to our school email newsletter | Kew

First time visit: View without clicking anything

Royal Botanic Gardens, Kew | Kew

Kew Science | Kew

Getting here | Kew

Illustrations and Artefacts Collections | Kew

Carnivorous plants explained: venus flytraps, pitcher plants & more | Kew

Digitising Kew's Collections | Kew

Balsa tree - Ochroma pyramidale | Kew

Wakehurst | Kew

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 2026

December 2025

Royal Botanic Gardens Kew

Title / URL	Issues
Sign up to our school email newsletter \| Kewwww.kew.org/learning/sign-up-school-newsletter	8
First time visit: View without clicking anythingwww.kew.org/	2
Royal Botanic Gardens, Kew \| Kewwww.kew.org/	2
Kew Science \| Kewwww.kew.org/science	2
Getting here \| Kewwww.kew.org/wakehurst/visit-wakehurst/getting-here	1
Illustrations and Artefacts Collections \| Kewwww.kew.org/science/collections-and-resources/collections/illustrations-and-artefacts-collection	1
Carnivorous plants explained: venus flytraps, pitcher plants & more \| Kewwww.kew.org/read-and-watch/carnivorous-plants	1
Digitising Kew's Collections \| Kewwww.kew.org/science/digitising-kews-collections	1
Balsa tree - Ochroma pyramidale \| Kewwww.kew.org/plants/balsa-tree	1
Wakehurst \| Kewwww.kew.org/wakehurst	1

Ensure form controls contrast sufficiently with their surroundings

Royal Botanic Gardens Kew

Where this issue has occurred