Login page accessibility

[missmatsuko]

Description

Some ares for accessibility improvements on the CP login page (/admin/login):

• Text in notice overlay when cookies are disabled has insufficient contrast (should be fixed with Update some color variables for WCAG contrast sass#1)
• If it's convenient, pull out h1 out of the form element. Elements in a form that aren't form inputs/buttons/labels can get missed in screen readers' form modes, but the page title would be announced when the page is first loaded anyways.
• When a site logo is uploaded, there should still be an h1 element containing the site name. It should be the site logo image with the site name as its alt value nested in an h1.
• It would be more clear if the login page form fields had persistent visible labels. Since it's a log-in form, users generally likely expect to enter a username/email and password. Maybe can be something to redesign for 4.0 if not sooner. Moved to: Persistent labels for login form fields #7296
• Required form fields are not announced to AT
• Password visibility toggle is not keyboard accessible
• The "Forgot your password" link doesn't have an href value so it isn't focusable/usable with the keyboard. Change to a valid a tag or button element. I would go with button since the URL isn't changing. Related: Keyboard accessibility- admin login #7287
• There should be some way to get back to the log-in form view after going to the reset password form view.
• The text should be updated for the forgot password form's submit button. It currently still says "Login". Should be changed to "Reset password" or similar.
• The "Craft CMS" image link has insufficient contrast of 1.98:1. Related: Improve contrast ratio #7289
• Don't disable the submit button. Instead, let the user submit the form and then display form errors if necessary.
• Use ARIA live regions to announce form errors and updates. Related: Error message loging screen #7288

Steps to reproduce

1. Go to /admin/login

Additional info

• Craft version: 3.5.16