Provide non-red highlight for Search field to make it look less like a field error

[jhaaaa]

When I hover over the Search field to enter a keyword, the field highlights in error, which makes it look like there is a field error or that something is broken in search:

Per Darick, let's use the highlight color that Tailwind uses: https://tailwindcss.com/docs/installation

[jhaaaa]

Addressed in https://github.com/xmtp/xmtp-dot-org/pull/195