If anyone could help me with this it would be much appreciated.
I am using the Mosaico theme purchased from Themeforest.
I am having difficulty with the column widths, particularly on the widget / sidebars. I have changed the width on the sidebar code, I changed the width of the Header on the sidebar I changed the width on all the list items too, but nothing is working.
Would anyone have any suggestions to what I am missing here?
Without seeing your site, impossible to even guess. But as you are using a commercial theme, you should contact ThemeForest and/or the developer for help.