David Borrink on "Input area right margins in TwentyTwelve tables"

I'm working on a TwentyTwelve child theme and have added a table with input areas that are text fields and text areas. The right margin of the text areas sets the field about 60 pixels from the right side of the table cell. I've checked many items in the CSS and cannot figure out where that 60 pixel margin is coming from. The input area CSS has no margin setting.

The .entry-content td CSS says,

.entry-content td, .comment-content td {
    border-top: 1px solid #BBBBBB;
    padding: 6px 10px 6px 0;
}

So there's no padding inside to force the right side of the table input area that far to the left.

Also, the text areas in this table are horribly narrow. About 40 pixels wide total with the little gripper icon in the lower right corner. I type in content and the box doesn't expand.

I haven't dealt with tables yet in TwentyTwelve so I'm wondering what's the trick to forcing my input fields to the full width of the table column yet keeping it responsive?