Fix FAB sheet backdrop when used in kirby-page

[mark-drastrup]

Which issue does this PR close?

This PR closes #2765

What is the new behavior?

The FAB sheet backdrop will take up the full height of the screen.

Does this PR introduce a breaking change?

• Yes
• No

Are there any additional context?

The cause of this issue is that one of the kirby-page div elements gets this styling from Ionic: transform: translateZ(0px). The backdrop component uses position: fixed, which under normal circumstances will position the element relative to the initial containing block established by the viewport, except when one of its ancestors has transform set to something other than none. See MDN documentation for position fixed.

Checklist:

The following tasks should be carried out in sequence in order to follow the process of contributing correctly.

Reminders

• Make sure you have implemented tests following the guidelines in: "The good: Test".
• Make sure you have updated the cookbook with examples and showcases (for bug fixes, enhancements & new components).

Review

• Determine if your changes are a fix, feature or breaking-change, and add the matching label to your PR. If it is tooling, dependency updates or similar, add ignore-for-release.
• Do a self-review.
• Request that the changes are code-reviewed
• Request that the changes are UX reviewed (only necessary if your PR introduces visual changes)

When the pull request has been approved it will be merged to develop by Team Kirby.