There are three (3) different ways to style an HTML element using css.

1. Inline styles.

2. Internal styles.

3. External styles.

  1. Inline styles : Inline styles are written inside the html tag using the style attribute.
    <div style='color:red;background-color:black;'>
 This is a div element.
</div>
  2. Internal styles : Internal styles are written in the same HTML page between the <style></style> tag.
    <html>
 <head>
  <style>
   div{
    color:red;
    background-color:black;
   }
  </style>
 </head>
 <body>
  <div>I am a block element.</div>
 </body>
</html>
    It's always preferred to write the <style></style> tag inside the head tag.
  3. External styles : in this way, we have to create a new file (style.css) and include it in the HTML file. 
    div{
 color:red;
 background-color:black;
}
    <html>
 <head>
  <link href="style.css" rel="stylesheet"/>
 </head>
 <body>
  <div>I am a block element.</div>
 </body>
</html>