Hello René.

Please note that the official support language is English, and we have to use Google Translator to try and understand other languages. Since a lot can be lost in translation, we apologize in advance if we misunderstood some segments of your message, and we also ask you to please translate your future messages to English.

Thank you for your understanding.

All you need to add is:

text-align: center !important;

So, your code should look like this:

.wpDataTablesWrapper table.wpDataTable.wpDataTableID-501 th {
font-size:19px;
font-weight:400;
text-align: center !important;
}
.wpDataTablesWrapper table.wpDataTable.wpDataTableID-501 td {
font-size:19px;
font-weight:400;
text-align: center !important;
}