To find the right div and table names, you will need to use the web inspector in your favorite browser (I find Safari’s web inspector to be the easies to use). Click on the crosshair icon and then click around the webpage. It will highlight the element in the source, and show any CSS in the sidebar, all of which is editable. Play around - you can’t ruin anything and it’s incredibly educational.
However, as I think those names are set by the SSS action itself, they shouldn’t change so that CSS should be 100% portable.
Regarding the contact form, check the width of “Box2” at the 480px breakpoint. It’s set to 150%, which obviously isn’t what you want it to be.