Use CSS property accent-color to tint form controls

[dhruvkb]

Fixes

Fixes #222 by @zackkrida

Description

This PR sets the trans-blue color as the accent color on the HTML root so that it automatically applies to form controls such as

• checkboxes
• radio buttons
• sliders
• progress bars

Other elements such as selections, markers etc. are tinted using the proper CSS rules associated with them.

Screenshots

With trans-blue accent:

Without accent, default:

Testing Instructions

1. Spin up the site using npm run dev.
2. See the new accent color.
3. In the dev tools toggle off the accent-color rule on the HTML root element.
4. See the default accent color.
5. Do step 3 repeatedly to see the slight difference between 2 and 4.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
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• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

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[sarayourfriend]

Tested in Firefox and Safari. Works great in Firefox but doesn't appear to do anything in Safari.

Was the intention to cover all browsers with this change?

[dhruvkb]

@sarayourfriend Safari does not support accent-color yet.

[sarayourfriend]

Okay! If all we're doing is using accent-color only then this LGTM. If we wanted to cover all browsers with uniform checkboxes we could copy the styles from Gutenberg's CheckboxControl component.

Otherwise LGTM!

[dhruvkb]

I don't think it's right to dismiss Safari. I'll check out the Gutenberg styles and see if we can bring Safari to parity. It'll have to be a separate PR because Gutenberg uses appearance: none and styles the component almost from scratch.

[zackkrida]

Cool! Looking into Safari is a welcome addition 👍