.chrome::search-text {
background: #ffff00; }
.chrome::search-text:current {
background: #ff9632; }
.firefox::search-text {
background: #ef0fff; color: white; }
.firefox::search-text:current {
background: #38d878; }

coming soon thanks to my colleagues at @igalia

https://groups.google.com/a/chromium.org/g/blink-dev/c/5FS_4mVQBLc