Adding CSS to HTML

External CSS

<!-- index.html -->

<head>
  <link rel="stylesheet" href="styles.css">
</head>
/* styles.css */

div {
  color: white;
  background-color: black;
}

p {
  color: red;
}

Internal CSS

<head>
  <style>
    div {
      color: white;
      background-color: black;
    }

    p {
      color: red;
    }
  </style>
</head>
<body>...</body>

Inline CSS

<body>
  <div style="color: white; background-color: black;">...</div>
</body>