Font size is just a matter of CSS.

td {
    font-size: 150%;
}

To add or override CSS: use the “Additional CSS” option in the customizer. https://codex.wordpress.org/CSS#Custom_CSS_in_WordPress

Learn to use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.

Thanks Steven for the quick answer!

I have copied the css into the “Advanced” tab (with and without a first dot), the size is the still the same…

How to make it work?

Friendly greetings!

Tamas

The CSS probably won’t work if that wasn’t the actual page in question. The link you gave above is a 404.

I am sorry!

The css is on the appropriate page.
Here it is:

Thanks!

Tamas

I have put what you suggested into the Customizing, Additional css and it WORKS!

Thanks a lot!

I have added css for borders, too:

td { font-size: 200%; }

table {
border: 3px solid black;
border-collapse: collapse;
}
td, th {
border: 1px solid #999;
}

THANKS A LOT!

greetings

Tamas