<html> <head> <style> th, td { background: #ddd; } table { border-collapse: collapse; } </style> </head> <body> <table border="1"> <tr><th>x</th><th colspan="2" class="a1 a2">A</th></tr> <tr><th>x</th><td class="a1">a1</td><td class="a2">a2</td></tr> </table> </body> </html>