Remove direct style attributs in index.php/index.html

The use of direct style attributes in the HTML of index.php and index.html prevents using an external CSS to do the styling.

Example: https://gitlab.com/paolobenve/myphotoshare/-/blob/master/web/index.php#L342

Reference from comment on LinuxFr: https://linuxfr.org/nodes/125761/comments/1870523