Справочник по Unity — 1. UI Toolkit

.header {
  font-size: 24px;
  color: #ffffff;
  unity-font-definition: "Assets/Fonts/Roboto-Bold.asset";
}

#score-value {
  color: #ffcc00;
}

.restart-btn:hover {
  background-color: #ff5555;
}

.score-container {
  flex-direction: row;
  align-items: center;
  margin: 10px;
}