fix: reduce mention highlight background opacity

[sachin-dul]

Description

Reduces the background opacity of mention highlight rows (both silent and loud variants) from full color to 40%

Tested the change locally and here is the screenshot of the reduced opacity,

Fixes #370

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

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

[Enitoni]

I'm very nitpicky, but try 35% or 30%? It still feels just a bit too bright for me.

[sachin-dul]

Tested at 35% and 30%, both still felt too bright. 25% strikes the right balance, noticeable but not distracting

Opacity at 25%,

[7w1]

Looks good thanks for contributing!