base.css provides a lot of what you need to style a site. You should become familar with its rules before making custom positioning or typographic adjustments. If you are missing particular style that should be there make a case for it's existance in a pull request.

Each tutorial will rely only on base.css. To get started, copy the starter template below that conatins a reference to the stylesheet:

<!DOCTYPE html>
<html>
<head>
  <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
  <meta charset=utf-8 />
  <title>NAME | Mapbox</title>
  <link rel='shortcut icon' href='path/to/favicon.ico' type='image/x-icon' />
  <link href='https://www.mapbox.com/base/latest/base.css' rel='stylesheet' />
</head>
<body>
  <!-- Content -->
</body>
</html>
On using custom styles

Sometimes styling is so unique to a problem that you need custom rules. This should generally be kept to a minimum and happen in a single document immediately proceeding the reference to base.css. Remember: any new style you introduce be sure to test and address styling for smaller screens and retina.