Stacked table borders do not line up when column count between tables does not match

When you have multiple tables with a border stacked on top of one another, the border line does not match up if the column count in the table doesnt match. So if table 1 has 1 row and 2 columns and table 2 has 1 row and 1 column, the borders of those tables will not line up unless you put colspan=2 on the first table.
````

test
test




test




test
test




test

````

Start by reproducing the supplied stacked-table HTML example and tracing how table widths, columns, and borders are laid out. Done means adjacent tables with different column counts have borders that line up without requiring a colspan workaround.

Written by the indexing model from the issue text.