What was the theme when the issue price was $508.95?
CREATE TABLE "18_k_gold_proof_lunar_hologram_coin_seri" (
  "year" real,
  "theme" text,
  "artist" text,
  "composition" text,
  "mintage" real,
  "issue_price" text
);
SELECT "theme" FROM "18_k_gold_proof_lunar_hologram_coin_seri" WHERE "issue_price"='$508.95';