[bug] Unit/vertical page is not responsive on mobile — tabs overflow and layout breaks

Expected Behaviour

When viewing a course unit (vertical) on a mobile device, the page layout — including the top navigation tabs (Course, Progress, Dates, Glossary, etc.) and the unit content area — should adapt responsively to the screen width, remaining fully usable and readable.

Actual Behaviour

On mobile devices, the course tab navigation overflows beyond the screen width and the overall page layout does not respond to the mobile viewport. Tabs are pushed off to the right and the content area does not reflow correctly, resulting in a broken and unusable layout on small screens.

https://www.loom.com/share/7ddb5a24ef6448959a54cd1c958140c6

Reproduction Steps

1. Open frontend-app-learning on a mobile/iPad device or a browser resized to a narrow mobile width (e.g. ~390px).
2. Navigate to any course and open a unit/vertical page.
3. Observe the top tab navigation overflowing off-screen and the broken page layout.

Additional Notes

• Reproduced on the current master.

Start by reproducing the issue in frontend-app-learning at a narrow viewport around 390px, then trace the course unit/vertical page and its top tab navigation. Confirm the layout reflows so the tabs and unit content remain usable and readable on mobile, and verify the result on a mobile or resized browser viewport.