refactor: update getDomElement

[davidglezz]

Pull request template

Update getDomElement to use newer CssInjector api

Motivation and context

• Dependencies. If any, specify:
• Open issue. If applicable, link:

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that causes existing functionality to not work as expected)
• Change requires a documentation update

What is the destination branch of this PR?

• Main
• Other. Specify:

How has this been tested?

Tests performed according to testing guidelines:

Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review on my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

[github-actions]

Check PR 615 preview 👀

S3 -> https://x.test.empathy.co/preview/615/index.html
R2 -> https://new-x.test.empathy.co/preview/615/index.html