Hello Karishma,
Try adding your custom styling in the very bottom textbox on the Fordson Colors page. Site Admin > Appearance > Fordson > Colours.
As for bringing over old CSS it might not work since different themes have different classes.
Thanks for taking a look at Fordson. I would take some time to just look over the default settings on the main fordson page where you can change the page layout and styling.
Once that is done maybe post a picture of your page and highlight the areas you want to change the color of.
Chris