Doc container doesn't stretch full page height any more

[Josh-Cena]

Have you read the Contributing Guidelines on issues?

• I have read the Contributing Guidelines on issues.

Prerequisites

• I'm using the latest version of Docusaurus.
• I have tried the npm run clear or yarn clear command.
• I have tried rm -rf node_modules yarn.lock package-lock.json and re-installing packages.
• I have tried creating a repro with https://new.docusaurus.io.
• I have read the console error message carefully (if applicable).

Description

After beta.18, the doc container doesn't take up the full page height any more.

Reproducible demo

No response

Steps to reproduce

1. Initialize site
2. Remove footer (non-critical, but makes the layout take up less height by itself)
3. Add a doc page without much content. Make sure the sidebar is short enough as well.

Expected behavior

This is the behavior in beta.17:

Actual behavior

This is the behavior in beta.18:

You can see this in our dogfooding test as well, just not so obvious:

https://docusaurus.io/tests/docs/doc-with-another-sidebar

Your environment

No response

Self-service

• I'd be willing to fix this bug myself.

[Josh-Cena]

Bisect leads up to #6925