The link you provided does not have any information on it. The page is no longer available.
I don’t understand the term “enqueue your css on admin area”. I put the above code into the text box of ‘edit page’ for the page I want it to appear. In every other site I have created this has been enough to add formatting etc. that are not included in the theme. I am sorry but if something more is required you are going to have to be very specific. I will need to add code to format all of the pages differently considering the very limited shortcakes provided for formatting and layout in this theme.