<style> .style-0{ background: red; } .style-1{ background: red; } .style-2{ background: blue; } .style-3{ background: green; } .style-4{ background: red; } .style-5{ background: blue; } .style-6{ background: green; } .style-7{ background: red; } .style-8{ background: blue; } .style-9{ background: green; } </style> <body> Рэндом фон. <script> document.body.className = 'style-' + parseInt(Math.random() * 10); </script> </body>