fix: TxFlow close button zindex

[usame-algan]

What it solves

Resolves #2429

How this PR fixes it

Removes the z-index for the close button

How to test it

1. Scroll down in the tx flow window
2. Try to press elements that are at the top of the screen e.g. nonce form
3. Observe that its possible to interact with them

Screenshots

Checklist

• I've tested the branch on mobile 📱
• I've documented how it affects the analytics (if at all) 📊
• I've written a unit/e2e test for it (if applicable) 🧑‍💻

[github-actions]

Branch preview

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https://close_z_index--walletweb.review-wallet-web.5afe.dev

[github-actions]

ESLint Summary View Full Report

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Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	0	N/A

• Result: ✅ success
• Annotations: 0 total

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^{Report generated by eslint-plus-action}

[katspaugh]

Thanks!

[francovenica]

Thanks, looks good.
I can click the nonce field and the X icon still works as intended.