ui/layout: expand collapsed vertical tabs on hover

[dusan-nikcevic]

• An issue exists where the maintainers agreed that this should be implemented
• I tested that my contribution works locally, and does not break anything
• If my contribution is non-trivial, I did not use AI to write most of it
• I understand that I will be permanently banned from interacting with this organization if I lied by checking any of these checkboxes.

Tested on (check one or more):

• Linux
• Windows
• macOS

---

Closes #915.

This adds an optional hover-expand mode for collapsed vertical tabs.

What changed:

• add a setting to expand collapsed vertical tabs on hover
• expand the collapsed vertical tab strip as an overlay instead of relaying out page content
• keep hover expansion/collapse behavior reliable with delay handling
• avoid hover-triggered expansion while interaction locks are active

Local verification:

• built Helium locally on Linux
• launched the built browser
• manually verified the collapsed vertical sidebar expands on hover

2026-02-27.00-12-54.online-video-cutter.com.mp4

[greptile-apps]

_{Last reviewed commit: 82b073c}

[cyfung1031]

This doesn’t seem to involve layout resizing on mouse hover. I hope the maintainers can review this.

[JackDerksen]

This doesn’t seem to involve layout resizing on mouse hover. I hope the maintainers can review this.

You mean resizing the main page layout in accordance to the sidebar expanding? That's visually jarring and more expensive than expanding as an overlay like this. If you want it to resize the page, just toggle the expansion with the button or cmd+s.

[LeastSaneDeveloper]

why hasn't this been merged yet?

[cyfung1031]

This doesn’t seem to involve layout resizing on mouse hover. I hope the maintainers can review this.

You mean resizing the main page layout in accordance to the sidebar expanding? That's visually jarring and more expensive than expanding as an overlay like this. If you want it to resize the page, just toggle the expansion with the button or cmd+s.

Sorry for my bad English. I was trying to say the opposite thing that this does not involve the layout recalculation so it should be good to proceed.

Hope maintainers can review and merge this PR.

[JackDerksen]

This doesn’t seem to involve layout resizing on mouse hover. I hope the maintainers can review this.

You mean resizing the main page layout in accordance to the sidebar expanding? That's visually jarring and more expensive than expanding as an overlay like this. If you want it to resize the page, just toggle the expansion with the button or cmd+s.

Sorry for my bad English. I was trying to say the opposite thing that this does not involve the layout recalculation so it should be good to proceed.

Hope maintainers can review and merge this PR.

Ah gotcha, my bad! I agree in that case. Looks like JJ's got the hover expansion sorted out pretty well for the zen mode, so they might be proceeding down that route instead?

[mousEHEHE]

would love to have this, very useful feature

[amsryq]

Ah gotcha, my bad! I agree in that case. Looks like JJ's got the hover expansion sorted out pretty well for the zen mode, so they might be proceeding down that route instead?

I'd argue this is not the same. Zen mode completely hides the tab bar AND address bar whereas this mode always shows it "collapsed".

[apotenza92]

Hi, I'm a bit late here but I think one small detail that's important for this feature is to make the hitbox zone of the expansion extend beyond the actual visible window of the application.

Brave Browser does not do this well, it only detects an 'expand sidebar' if the mouse cursor is precisely inside the compact vertical tabs side bar.

But apps like Arc or Zen detect a more loose 'mouse went past the edge of the sidebar' and this causes it to expand too.

Essentially Brave's implementation of this auto-expand on hover feature is a bit too finicky whereas Arc and Zen 'feel' better from a UX perspective.

Brave:
Note how you cannot overshoot the sidebar with your mouse cursor so it's very 'strict':
https://github.com/user-attachments/assets/01548052-6f56-40f9-99d1-5acbadbd1518

Zen:
Note how you can overshoot the edge of the window and still see the sidebar expand:
https://github.com/user-attachments/assets/ea90b340-d8d6-4cef-ade3-44aaa333dbbe

I understand this is also likely because Brave is showing the compact sidebar vs showing no visible compact sidebar but I think this behaviour should be consistent regardless of if the sidebar is visible in compact form or not.

[aryankeluskar]

One thing Brave does well that Zen doesn't is the expanding transition. Zen's has some sort of ease-in or ease-out which makes it very slow to expand the sidebar relative to Brave, and sometimes it's annoying.

Brave:

Screen.Recording.2026-04-27.at.5.44.13.AM.mov

Zen:

Screen.Recording.2026-04-27.at.5.48.35.AM.mov

Zen also does not show favicons, so I have to hover and then find the tab I wanna go to.

[apotenza92]

Trying out the new Zen mode. I hate how slowly I need to move my mouse to the sidebar to activate the expand on hover. I really miss how quickly I can fling my mouse haphazardly to the sidebar on Zen Browser and Arc. Seems too finicky still (0.11.6.1).