It looks like a few more things need 100% widths.
Update this line in the css:
form.NewFromBlank_Default div.columnGroup, form.NewFromBlank_Default textarea.formTextarea_Medium, form.NewFromBlank_Default input.formTextfield_Medium, form.NewFromBlank_Default select.formMenufield_Medium, form.NewFromBlank_Default div.wideColumnGroup,
form.NewFromBlank_Default input.formButton {
width: 100%;
box-sizing: border-box;
}
to:
form.NewFromBlank_Default div.columnGroup, form.NewFromBlank_Default textarea.formTextarea_Medium, form.NewFromBlank_Default input.formTextfield_Medium, form.NewFromBlank_Default select.formMenufield_Medium, form.NewFromBlank_Default div.wideColumnGroup, form.NewFromBlank_Default input.formButton, form.NewFromBlank_Default div.fullColumnGroup,form.NewFromBlank_Default input.formTextfield_Large {
width: 100%;
box-sizing: border-box;
}