How do I render a form as a table?
I had forgotten about the table-cell and table-row diplay properties. Despite the fact that CSS is off topic, the way to do it given Drupal's  form class structure is:

.form-no-label {
    display: table-cell;
}
label {
    display: table-cell;
}
.container-inline {
    display: table-cell;
}
.label {
    display: table-cell;
}
.form-item {
    display: table-row;
}