[BUG] Hover color contrast too high for Discover histogram

[brucejxz]

Describe the bug

When hovering over the histogram in Discover with dark mode enabled, the hover color is bright white, which is a huge contrast to the dark background.

To Reproduce
Steps to reproduce the behavior:

1. Go to Discover
2. Move the mouse around the histogram panel at the top

Expected behavior
It would look more polished if the hover color was more subtle and not such a large contrast with the background color.

OpenSearch Version
2.13.0

Dashboards Version
2.13.0

Plugins

Reproducible at https://playground.opensearch.org

Screenshots

Host/Environment (please complete the following information):

• OS: macOS 14.4
• Browser and version: Safari 17.4

Additional context

N/A

[abbyhu2000]

@kgcreative @opensearch-project/opensearch-ux Can we have some UX feedback here?