fix: hidden backTop button on mobile device

[whale2002]

Maybe...emm, this is the easiest way I can think

[changeset-bot]

⚠️ No Changeset found

Latest commit: f1cbe8b

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated
island	✅ Ready (Inspect)	Visit Preview	Nov 1, 2022 at 8:26AM (UTC)

[netlify]

✅ Deploy Preview for jade-conkies-8119e7 ready!

Name	Link
🔨 Latest commit	f1cbe8b
🔍 Latest deploy log	https://app.netlify.com/sites/jade-conkies-8119e7/deploys/6360d7dc94428500093412c0
😎 Deploy Preview	https://deploy-preview-136--jade-conkies-8119e7.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[sanyuan0704]

Thank you.