785 colour contrast readonly and placeholder text

[dhinrichs-scottlogic]

Description

Ensure all color contrast passes, including disabled buttons, readOnly fields (e.g. config inputs) and placeholder text (e.g. chat input). Closes #785

Screenshots

Additional context

Colour contrast issues for placeholder text are easily missed by automated tools, but colour contrast ratios should still pass for placeholder text and inactive input text.

Notes

• adjusted the --main-input-inactive-text-colour to pass but be less close to black
• adjusted the --level-button-colour-disabled colour to provide better contrast (it technically passed before because the text is bold, but just nudging it to also pass 4.5:1).
• Added placeholder pseudo selector to css to adjust textinput placeholder text colour

Checklist

Have you done the following?

• Linked the relevant Issue
• Added tests
• Ensured the workflow steps are passing

[pmarsh-scottlogic]

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