How many columns are you planning to display? The 'Simple Checkbox set selector' is waiting for approval in the App Store for who just want to render a simple list of checkboxes and don't want to be bothered with a table.
It renders a checkbox list in a bootstrap html structure and renders a div element for each object instead of a table which the checkbox set selector(Table) does.
You can find the new widget here https://github.com/mendix/SimpleCheckboxSetSelector/releases. Maybe you already want to try it out.
If you want to override the table-bordered bootstrap styling you need be very specific. This should work:
.wgt-CheckboxSetSelector .table-bordered,
.wgt-CheckboxSetSelector .table-bordered>tbody>tr>td,
.wgt-CheckboxSetSelector .table-bordered>tbody>tr>th,
.wgt-CheckboxSetSelector .table-bordered>tfoot>tr>td,
.wgt-CheckboxSetSelector .table-bordered>tfoot>tr>th,
.wgt-CheckboxSetSelector .table-bordered>thead>tr>td,
.wgt-CheckboxSetSelector .table-bordered>thead>tr>th {
border: 0;
}
Im not 100% if ".wgt-CheckboxSetSelector" is the class on the widget, but you can always set a custom class on the widget and replace " .wgt-CheckboxSetSelector" with that name in your css.
In my situation I added a class to the widget and targeted that specific instance. Here's the snippet.
.checkboxsetselectoralignment .table-bordered>tbody>tr>td {
border: 0;
}