Lichess user style for custom board

lichess.board.css

cg-board::before {
  background-color: #e2ae83;
  background-image: url('data:image/svg+xml;base64,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');
  filter: unset;
}

cg-wrap coords:nth-child(odd) coord:nth-child(odd),
cg-wrap.orientation-black coords:nth-child(odd) coord:nth-child(even),
cg-wrap coords.files:nth-child(even) coord:nth-child(odd),
cg-wrap.orientation-black coords.files:nth-child(even) coord:nth-child(even) {
  color: #edd6b0;
}

cg-wrap coords:nth-child(odd) coord:nth-child(even),
cg-wrap.orientation-black coords:nth-child(odd) coord:nth-child(odd),
cg-wrap coords.files:nth-child(even) coord:nth-child(even),
cg-wrap.orientation-black coords.files:nth-child(even) coord:nth-child(odd) {
  color: #b88762;
}

cg-board square.last-move {
  background-color: rgba(246, 235, 114, 0.6);
}
cg-board square.selected {
  background-color: rgba(90, 167, 204, 0.6);
}
cg-board square.move-dest, cg-board square.premove-dest {
  background: radial-gradient(rgba(87, 48, 23, 0.6) 19%, rgba(0, 0, 0, 0) 20%);
}

cg-board square.oc {
  background: unset;
  background-color: rgba(255, 125, 125, 0.6);
}

cg-board square.current-premove, cg-board square.last-premove {
  background-color: rgba(187, 55, 188, 0.6);
}

Now with a shiny project to help you configure it easily:
https://github.com/mobeigi/lichess-tailor

Website:
https://lichess-tailor.mobeigi.io/