Harmonize the icon color with the standard color (#201)

Changes the `expansion-card.svg` code from `jp-icon0` class to
`jp-icon3` which is more appropriate for sidebar/window icons in
JupyterLab design style.

Fixes #199

#### Light theme

| Before | After |
| -- | -- |
|
![image](https://github.com/rapidsai/jupyterlab-nvdashboard/assets/5832902/0d660026-05ff-46d2-b3f2-82018a59c596)
|
![image](https://github.com/rapidsai/jupyterlab-nvdashboard/assets/5832902/86817c02-751d-45c5-aeed-032a4700a31e)
|

#### Dark theme

| Before | After |
| -- | -- |
|
![image](https://github.com/rapidsai/jupyterlab-nvdashboard/assets/5832902/8ace1694-a9d8-4053-8047-233f26e9362c)
|
![image](https://github.com/rapidsai/jupyterlab-nvdashboard/assets/5832902/bccf43fa-5f51-4dcd-8713-1299864ccd11)
|

#### High contrast dark theme

| Before | After |
| -- | -- |
|
![image](https://github.com/rapidsai/jupyterlab-nvdashboard/assets/5832902/db8e4eea-f767-4e64-8672-8a799e8baf0d)
|
![image](https://github.com/rapidsai/jupyterlab-nvdashboard/assets/5832902/eeb6f36d-6561-4074-9bb0-550701c9a146)
|

Co-authored-by: Ajay Thorve <[email protected]>