[Dashboards][SecuritySolution] Custom dashboards have vertical space issues and inconsistencies in security solution

[ghudgins]

Kibana version: main as of 21 November 2024

Browser version: Chromium

Original install method (e.g. download page, yum, from source, etc.): from source

Describe the bug:

• Security Solutions Dashboard app is injecting a heading level 1 of "Editing new dashboard" or the name of the dashboard in edit and view mode breaking up the page and putting a heading level 1 underneath some of the page's content (anti pattern for web design).
• There is a missing gray background on dashboard canvas in security solution

Steps to reproduce:

1. Go to "Dashboards" in security solution
2. Click "Create new dashboard"

Result:

1. "Editing new dashboard" heading 1 is showing beneath unified search
2. Background is inconsistent with observability (white background on dashboard canvas)

Expected behavior:

1. No heading 1 is shown (see o11y comparison in screenshot
2. Background is gray (see o11y comparison in screenshot)

Screenshots (if relevant):

Any additional context:

Discussed with @dimadavid https://elastic.slack.com/archives/C07SJJ23865/p1732202088472599

It's probably due to the out of the box security dashboards leaking into the custom dashboards. Hoping it's an easy fix 🙏

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)