custom.css: make donation block larger on small screens

See merge request lqdn-interne/don!36

Resolve "changer le type de don coché par défaut"

Closes #43

See merge request lqdn-interne/don!35

Use HMAC-SHA256 instead of SHA1

Closes #29

See merge request lqdn-interne/don!5

Resolve "Nouveau front"

Closes #32

See merge request lqdn-interne/don!33

Resolve "Nouveau front"

Closes #32

See merge request lqdn-interne/don!32

Ajout des petits triangles

See merge request lqdn-interne/don!30

# Conflicts:
#   app/view/user/perso.html
#   www/static/css/custom.css