body {
  margin: 0;
  background: #222;
  color: #fff;
  font-family: Arial, sans-serif;
  overflow: hidden;
  position: fixed;
  width: 100%;
  height: 100%;
}
#gameCanvas {
  display: block;
  margin: 30px auto;
  background: #333;
  border: 3px solid #444;
  box-shadow: 0 0 20px #000;
}
#ui {
  text-align: center;
  margin-top: -20px;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.buttons {
  display: flex;
  gap: 10px;
  justify-content: center;
  align-items: center;
}

#coins {
  background: rgba(0, 0, 0, 0.3);
  padding: 8px 16px;
  border-radius: 5px;
  font-weight: bold;
  color: #ffd700;
}

#upgradeBtn, #knifeUpgradeBtn, #resetBtn {
  background: #4caf50;
  color: #fff;
  border: none;
  padding: 8px 16px;
  font-size: 16px;
  border-radius: 5px;
  cursor: pointer;
}

#knifeUpgradeBtn {
  background: #2196F3;
}

#resetBtn {
  background: #f44336;
}

#upgradeBtn:disabled, #knifeUpgradeBtn:disabled {
  background: #888;
  cursor: not-allowed;
}