@correct-colors: #9be9a8, #40c463, #30a14e, #216e39;
@incorrect-colors: #ff8c8c, #ff4d4f, #ff1a1a, #d40d0d;

.generate-heat-rules(@class, @colors) {
  each(@colors, {
    .@{class}[data-level="@{index}"] {
      background-color: @value;
    }
  });
}

.generate-heat-rules(correct-heat, @correct-colors);
.generate-heat-rules(incorrect-heat, @incorrect-colors);