publishing | ONS Digital

Data | ONS Digital

ONS Digital | Page 38 | Blog for the ONS Digital Content teams

ONS Digital | Page 41 | Blog for the ONS Digital Content teams

website | ONS Digital

ONS Digital | Page 5 | Blog for the ONS Digital Content teams

opendata | ONS Digital

ONS Digital | Page 3 | Blog for the ONS Digital Content teams

Data Discovery | ONS Digital

ONS Digital | Page 6 | Blog for the ONS Digital Content teams

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

May 2025

April 2025

ONS Digital

Title / URL	Issues
publishing \| ONS Digitaldigitalblog.ons.gov.uk/category/publishing/	3
Data \| ONS Digitaldigitalblog.ons.gov.uk/category/data/	3
ONS Digital \| Page 38 \| Blog for the ONS Digital Content teamsdigitalblog.ons.gov.uk/page/38/	3
ONS Digital \| Page 41 \| Blog for the ONS Digital Content teamsdigitalblog.ons.gov.uk/page/41/	3
website \| ONS Digitaldigitalblog.ons.gov.uk/category/website/	3
ONS Digital \| Page 5 \| Blog for the ONS Digital Content teamsdigitalblog.ons.gov.uk/page/5/	3
opendata \| ONS Digitaldigitalblog.ons.gov.uk/category/opendata/	3
ONS Digital \| Page 3 \| Blog for the ONS Digital Content teamsdigitalblog.ons.gov.uk/page/3/	3
Data Discovery \| ONS Digitaldigitalblog.ons.gov.uk/category/data-discovery/	3
ONS Digital \| Page 6 \| Blog for the ONS Digital Content teamsdigitalblog.ons.gov.uk/page/6/	3

Ensure form controls contrast sufficiently with their surroundings

ONS Digital

Where this issue has occurred