I am really terrible at CSS/UI design (I am a C#/.NET developer) so in Sitefinity v. 3.7 SP4 I used to always work backwards from a site that a client liked and then eliminate portions of the page to create my final Master Template in SItefinity.
However, I tried following the same process in Sitefinity v. 7.0 and I ended up in an infinite loop that basically completely hung the system!! I created my Master Page file directly using Sitefinity Thunder by copying and pasting the entire HTML from another site, created a Page Template in Sitefinity and then attempted to create a Page based on the newly created Page Template.
However, as soon as I attempted to edit the Page, the editor hung forever in an infinite loop. I could not get out of the screen except by hitting the browser back button at which point the page I created to begin editing completely disappeared.
I have attached a screenshot for your review.