Injecting HTML-formatet text

If you need to create nice formatet incidents in ServiceNow, you cant just update the data-field with an HTML formattet document. I found that styling via classes as shown below worked fine.

.cbas *{border-style: solid;border-color: black;} 
.cbas {border-collapse: collapse; WIDTH:100%;} 
.cbas TH,TD{border-width: 2px;padding: 2px;} 
.cbas TH{background-color:darkgray} 
.cbas TD{background-color:white; vertical-align: top} 
</style> <br /> Some tekst <b>bold</b> 
<TABLE class="cbas">
<tr><th>Brugernavn</th> <th>Fornavn</th> <th>Efternavn</th> <th>Stilling</th> <th>Telefonnr</th> <th>Firmakode</th> <th>Afd.kode</th> </tr>
<BR /><BR /> <BR /> (V3-2019-SEP-02)

The problem is that ServiceNow injects this code into its web page and if you just style the TABLE, TH and TD elements you overwrite the style used by ServiceNow.