Google map is not responsive

Hello!

I noticed that google map has a fixed dimension of 400x300px. Which destroy my mobile layout when visiting from a mobile (too large horizontally). I tried changing the width of the google map parent div to 100% width. However, because Google map size is set by html/php to be 400x300px, when zooming or dezooming, only an area of 400x300px is loaded in the map, leaving a grey space around inside the map !

Do you know where to set and change the width in the php code ? (Which file of event manager has to be modified ?)

Thank you !