You can adjust the following styles. Remove any line to revert it back it’s default value.
/**
* Simple Table
* Border Styling
* From Will-Myers.com
**/
div[data-wm-plugin="simple-table"] {
--simple-table-border-width: 2px;
--table-border-type: solid;
--table-border-color: white;
--table-border-radius: 12px;
}