* index page: margin top is 24% of the view port.
avoid to scroll a small screen,
center the content in the middle of the screen
* link to preferences at the same height same the input fields
* increase the category tab heighs
* increase the margin bottom of the query field
* in the results, change the h3 margin top and bottom to 0.4rem (6px)
* move the back to top button slightly on the right when the results are only images
When an image is selected, the detail with the full size image is displayed
on the right side of the screen (or full screen on tablet and phone).
When Javascript is disabled, the thumbnail is a linked to the full size image,
as it was before.
When the image proxy is enabled, the full size image is also proxied,
in consequence this commit increases the bandwidth usage of instances.
The detail can be closed by the close button or the Esc key.
It is possible to go to the next and previous images using the j and k keys
or the button on the top right of the screen.
