Maintenance: report ess france fixes

This MR fixes several issues related to colors, fonts and i18n. It introduces some css variables that are fixed by default used variables from Hubl.

:root{
  --color-event-text: var(--color-grey-4);
  --color-event-icon: var(--color-icon);
  --color--event-title: var(--color-title);
  --font-family-event-title-h1: var(--font-family-title-h1);
}

closes #4, #12

mentioned in issue #4

mentioned in issue #12

changed the description

@fabien4vo my tests were not concluding :-)

Lots of regression, if we can check that (the way I am testing it, the state of my app vs yours) together tomorrow, let me know !

Not tomorrow, sorry (it's Wednesday, kid's day). Thursday before 10am or after 4pm ?