<!DOCTYPE html> <html> <head> <head> <style> table table { border-collapse: collapse; border-style: solid; border-width: 10px; border-color: green } </style> </head> </head> <body> <table><tr> <td> <table> <tr><td></td></tr> </table> <table> <tr><td></td></tr> </table> </td> </tr></table> </body> </html>