如何使单独的按钮具有不同的颜色

<button class="red-button">Red Button</button>
<button class="blue-button">Blue Button</button>

.red-button {
  background-color: red;
}

.blue-button {
  background-color: blue;
}

<button id="red-button">Red Button</button>
<button id="blue-button">Blue Button</button>

var redButton = document.getElementById("red-button");
redButton.style.backgroundColor = "red";

var blueButton = document.getElementById("blue-button");
blueButton.style.backgroundColor = "blue";