ページ内検索バー　こんなんでどうかな

:root[lwtheme-image] .browserContainer > findbar {
background-image: none !important;
background-color: var(--identity-icon-color, transparent) !important;
}
:root[lwtheme-image] findbar .findbar-textbox {
--input-border-color: color-mix(in srgb, currentColor 41%, transparent) !important;
}