quarto_theme

As of this rendering, quarto websites render all pages under the site-wide bootstrap 5 theme, and ignores themes defined for individual pages.

For example, the theme for this website is defined in _quarto.yml as:

format:
  html:
    theme: cosmo
    css: css/nav.css

And, the theme for this page is defined in the yml header of this .qmd file as:

format: 
  html: 
    theme: minty

However, the minty theme is not overriding the site-wide cosmo theme for this page. Individual pages can be custom themed by including a css file and modifying bootstrap defaults, or by declaring new css classes.