Improve design

[GuillaumeGomez]

This UI change brins some improvements:

• The layout was not great: you had less reading width when on desktop compared to mobile.
• The width of the content was changing too much (and not efficient as mentioned above).
• It is now more clear how to go back to homepage with a visually distinct header.

Here what it looks like now:

cc @CohenArthur

[CohenArthur]

looks amazing :D thank you @GuillaumeGomez !!