GeezerVison

Link to issue

Closes #4847

Continuation of PR #4848 by @mishrakushal

Description of change

Add <!doctype html> at top of HTML template for compliance with modern web standards.

Demo

n/a

Testing strategy

Call fig.to_html() and verify that the generated HTML file has <!doctype html> at the very top.

Additional information (optional)

Updated unit tests accordingly.

Note: Adding <!doctype html> changed the chart rendering behaviour and made charts render at 450px high rather than filling the browser window. To keep the existing behaviour, this PR adds a small HTML snippet to the template:

<style>html, body {{height: 100%;}}</style>

Guidelines

• I have reviewed the pull request guidelines and the Code of Conduct and confirm that this PR follows them.
• I have added an entry to the changelog if needed (not required for documentation PRs).