fix(css): insert styles in the same position

[sapphi-red]

Description

When a style was injected by JS, the order was inconsistent between dev and build.

While this works for the current style-injection approach, this is not feasible by the adoptedStyleSheets approach (currently disabled due to low perf) because adoptedStyleSheets are ordered after all the other style sheets.
I didn't touch the adoptedStyleSheets approach but maybe we can simply remove this.

fixes #11760

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the PR Title Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.