<button commandfor="number" command="--decrement">-</button>

<input type="number"
        id="number"
        min="0"
        value="0">

<button commandfor="number" command="--increment">+</button>

numberInput.addEventListener("command", (event) => {
  if (event.command === "--increment") {
    numberInput.stepUp();
  }
  if (event.command === "--decrement") {
    numberInput.stepDown();
  }
  updateDecrementButton();
});