Isolated build header collapses

[Mpdreamz]

cursorful-video-1742997420946.mp4

The header collapses somewhere in the middle of the page.

Not a high priority but it looks odd.

[reakaleek]

This was fixed during #892 and #896.

You can see the fixed behaviour in the latest build: https://docs-v3-preview.elastic.dev/elastic/docs-builder/tree/main/syntax/links