Making a web app responsive

We are building a pwa (progressive web app) and we want to hire a freelancer to make our app responsive as it is not well done currently.
Here is the website : [URL visible pour les membres Pro]
To connect you can use this id/password :
id : Freelance
mdp : Freelance

We are on quite low budget, and part of the job has already been done, so we're expecting competitive offers.

(We are a french team)