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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

July 2025

June 2025

City of South San Francisco

Title / URL	Issues
City Newsletter - City of South San Franciscowww.ssf.net/Our-City/City-Newsletter	1
首頁 - 南舊金山市www.ssf.net/Home?lang_update=638796515887633958	1
City Calendar - City of South San Franciscowww.ssf.net/Our-City/City-Calendar	1
Our City - City of South San Franciscowww.ssf.net/Our-City	1
Home - City of South San Franciscowww.ssf.net/Home	1
Online Pay and Services - City of South San Franciscowww.ssf.net/Services/Online-Pay-and-Services	1
Boards & Commissions - City of South San Franciscowww.ssf.net/Government/Boards-Commissions	1
First time visit: View without clicking anythingwww.ssf.net/Home	1
Inicio - Ciudad del Sur de San Franciscowww.ssf.net/Home?lang_update=638796515459964630	1
About SSF - City of South San Franciscowww.ssf.net/Our-City/Biotech/About-SSF	1

Ensure form controls contrast sufficiently with their surroundings

City of South San Francisco

Where this issue has occurred