How to remove a blue tint over a sidebar search box in Sphinx Read The Docs theme?

I am building documentation for my Python package with Sphinx (9.1.0) using Read the Docs theme (3.1.0). I have adjusted colors on my sidebar: the header from inside the conf.py file:

html_theme_options = { "style_nav_header_background": colors["red"], }

and the bar below it via my custom.css file which gets loaded during the docs generation:

.wy-nav-side { background-color: var(--grey5); }

However, please note the effect in the attached picture. There is still thin blue tint over the search box. Is there any way to remove it?