fluid=True appeared to work well and also solved my other issue at Bug: html.Div and dbc.Row output does not vertically align which I have now noticed is caused by the .row
margin: 0; (thought I had double checked that)
However on each page new page click (I am using a multi-page app with dbc.NavLink) the whole page gets adjusted about 10 pixels to the right. I thought this could be caused by dbc.Container not gelling with my other px-# and mx-# settings but even after redefining them all to dummy names, my app still slides to the right with every page change.
Going back to html.Div 
and actually living with the horizontal browser play until this can be figured out.