Change front page layout for Quarto Book

Anyone know to pass in a custom layout template for Quarto HTML book?

This is the default look for a Quarto book:

Here is the _quarto.yml

project:
  type: book

book:
  title: An example report
  subtitle: The subtitle
  author:
    - name: Jane Doe
      affiliations:
        - name: University of XXX
          department: Department of YYY
    - name: Eva Nováková
      affiliations:
        - name: University of XXX
          department: Department of YYY
    - name: Matti Meikäläinen
      affiliations:
        - name: University of XXX
          department: Department of YYY
  chapters:
    - index.qmd
    - text/conclusion.qmd
    - references.qmd

format:
  html:
    theme: cosmo
    toc: true
    toc-depth: 3

In Jekyll site, I am used to using _layouts/default.html to override the default layout template. But I can't figure out how to do that in Quarto.

For PDF output, I discovered that this works for passing in a template:

  pdf:
    documentclass: scrbook
    classoption: ["oneside"]
    template-partials: ["partials/before-body.tex"]

In the template (passed in via template-partials: you can use variables for the YAML like {{author.affiliation}} for example and create your own custom title page. But I haven't found anything like templates-partials for the HTML.