[field] accessibility: Example fails non-text contrast requirement

[grace-snow]

Bug report

Current behavior

The input in the Field component example is very difficult to see because the input border has such low contrast against adjacent colours. As a result, this fails WCAG 2.2 Success Criterion 1.4.11 Non-text Contrast

Expected behavior

The border has a near-transparent colour (oklch(0.12 0.04 264.01 / 0.07)) but must have at least a 3:1 contrast ratio against adjacent colours. This is the requirement for all UI components and meaningful graphics.

Reproducible example

1. Navigate to the Field component example
2. Use a tool like the Colour contrast analyser to colour pick the border colour and adjacent background colour
3. Note the ratio

Base UI version

v1.2.0

Which browser are you using?

Chrome

Which OS are you using?

Mac OS

Which assistive tech are you using (if applicable)?

N/A

Additional context

Ensure all component examples meet contrast requirements to demonstrate best practices.

[linear]

BAS-449

[aarongarciah]

We're working on some docs UI improvements that include revising all colors used in demos, so we'll likely tackle this in the upcoming weeks.