Fix tables border in html viewer gadget

See merge request !1705
13 jobs for erp5_drone_simulator in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

01:07:42

failed ERP5.UnitTest-Master

02:00:26

failed ERP5.UnitTest-Master.Medusa

01:13:37

passed SlapOS.Eggs.UnitTest-Master.Python2

00:12:45

passed SlapOS.Eggs.UnitTest-Master.Python3

00:14:46

passed ERP5.CodingStyleTest-Master

00:54:41

passed ERP5.CodingStyleTest-Master

00:50:36

failed ERP5.UnitTest-Master

01:29:47

failed ERP5.UnitTest-Master

01:18:33

passed SlapOS.Eggs.UnitTest-Master.Python2

00:12:11

passed SlapOS.Eggs.UnitTest-Master.Python2

00:13:52

passed SlapOS.Eggs.UnitTest-Master.Python3

00:13:41

passed SlapOS.Eggs.UnitTest-Master.Python3

00:14:00