Свойство tab-size

tab-size: число;

<!DOCTYPE html>
<html lang='ru'>
<head>
<meta charset='UTF-8'>
<meta name='viewport' content='width=device-width, initial-scale=1.0'>
<title>Document</title>
</head>
<body>
<style>
 pre {
 -o-tab-size: 10; /* Opera */
 -moz-tab-size: 10; /* Firefox */
 tab-size: 10;
 }
 </style>
 <pre>1 2 3 4 5 6 7 8 9 10</pre>
</body>
</html>