Reduce height of chat window so it fits better in iframe

[zackproser]

Problem

We got a report from @krugster that the chat window height was too tall in the iframed demo on the docs, causing the UI to be unwieldy.

Solution

Shrink the height of the chat window by 150px.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

This change has been validated locally and will be validated in a preview environment and production.