Support the MBL | Marine Biological Laboratory

Contact HR | Marine Biological Laboratory

Advisory Bodies | Marine Biological Laboratory

Contact Us | Marine Biological Laboratory

Staff Toolbox | Marine Biological Laboratory

About the MBL | Marine Biological Laboratory

Our Community | Marine Biological Laboratory

MBL Society | Marine Biological Laboratory

Seeing Life Exhibit | Marine Biological Laboratory

MBL Community | Marine Biological Laboratory

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

October 2025

September 2025

Marine Biological Laboratory

Title / URL	Issues
Support the MBL \| Marine Biological Laboratorywww.mbl.edu/give	8
Contact HR \| Marine Biological Laboratorywww.mbl.edu/about/careers-internships/contact-hr	1
Advisory Bodies \| Marine Biological Laboratorywww.mbl.edu/about/advisory-bodies	1
Contact Us \| Marine Biological Laboratorywww.mbl.edu/contact	1
Staff Toolbox \| Marine Biological Laboratorywww.mbl.edu/about/careers-internships/staff-toolbox	1
About the MBL \| Marine Biological Laboratorywww.mbl.edu/about	1
Our Community \| Marine Biological Laboratorywww.mbl.edu/about/careers-internships/our-community	1
MBL Society \| Marine Biological Laboratorywww.mbl.edu/about/advisory-bodies/mbl-society	1
Seeing Life Exhibit \| Marine Biological Laboratorywww.mbl.edu/about/history-archives/seeing-life-exhibit	1
MBL Community \| Marine Biological Laboratorywww.mbl.edu/about/mbl-community	1

Ensure form controls contrast sufficiently with their surroundings

Marine Biological Laboratory

Where this issue has occurred