Hello Iryna.

Thank you for reaching out to us.

You can only change the colors for all modals (edit, new entry, and check-box) with this CSS:

.wpdt-c .btn-danger {
    background-color: green;
    border-color: green;
}
.wpdt-c .btn-success {
    background-color: blue;
    border-color: blue;
}

And the modal will look like this:

As for the check-box itself, you can use this CSS:

#wdt-frontend-modal .wdt_checkbox_option input[type="checkbox"]:checked:before, #wdt-frontend-modal .wdt-search-filters-button-container .wdt_checkbox_option input[type="checkbox"]:checked:before {
    background-color: red;
    border-color: red;
}

And it will look like this:

You're welcome Iryna, sorry for the delay.

You can use this CSS to color the checkboxes outside of the modal:

.wpdt-c .wpDataTableFilterSection .wdt_checkbox_option input[type=checkbox]:checked::before {
   border: red;
   background: red;
}