Leo side panel scrollbar broken after 1.64.x builds

[MadhaviSeelam]

Description

It looks like Leo panel scrollbar is broken after 1.64.x builds. In a new profile when clicked on Leo icon in a new tab, Intro text is shown however, bottom text with toggle is hidden ("Shape answers based on the page's content`). In some cases, Intro text hidden or Session expired message is not shown. These issues could be solved with scrollbar is available as before.
Note: scrollbar is available when queried an article with Leo.

I have filed following related issues:

#41136
#40910

Steps to reproduce

1. Install 1.70.117
2. launch Brave
3. click Leo icon in the tool bar or (via sidepanel)

Actual result

example	example

Expected result

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Brave	1.70.117 Chromium: 129.0.6668.59 (Official Build) (64-bit)
Revision	5d4da8332eb061f79bb47ec5b0bf595600fdcd55
OS	Windows 11 Version 23H2 (Build 22631.4169)

Channel information

• release (stable)
• beta
• nightly

Reproducibility

• with Brave Shields disabled
• with Brave Rewards disabled
• in the latest version of Chrome

Miscellaneous information

@mattmcalister
cc: @rebron @qa