fix(register): scroll focused form fields into view above the anonymous consent banner

Problem

The cx-anonymous-consent-management-banner component renders as a position: fixed; bottom: 0 overlay at the bottom of the viewport. When a user navigates the registration form using the Tab key, the browser's native focus-scroll behaviour does not account for the fixed banner, causing focused form fields to be obscured behind it.

Solution

A pure CSS fix was applied using two complementary browser-native scroll properties:

• scroll-padding-bottom on the html element — instructs the browser to reserve bottom clearance equal to the banner height whenever it auto-scrolls a focused element into view. Applied conditionally via :has() so it is only active when the banner is actually visible.
• scroll-margin-bottom on register form groups and focusable elements — ensures each focusable element declares its own required bottom margin from the viewport edge, centering it in the visible area above the banner on Tab focus.

A shared SCSS variable ($cx-anonymous-consent-banner-height) was introduced to avoid magic numbers and keep all related offsets in sync.

Notes

• No JavaScript changes — the fix is entirely CSS-based.
• The $cx-anonymous-consent-banner-height variable uses rem units (instead of px) to respect the user's browser font-size settings, which aligns with the existing codebase conventions and improves accessibility.
• The !default flag allows consuming applications or custom themes to override the value if needed.
• The :has() selector ensures scroll-padding-bottom is only applied when the banner is rendered and visible, avoiding any side effects on other pages.

QA steps

1. authorizationCodeFlowByDefault feature flag needs to be set to false in order to make the registration page visible.
2. Click on Sign in / Registration and try to use Tab button to navigate between elements.
3. They should be positioned in the center of the page after every Tab button press.