Hi there Sacha,
Thanks for getting in touch with us! It looks like there’s a conflict with the style from the theme you are using (by default this button is not fill width in our stylesheet) 🙁
I see your site is now using the horizontal layout for FilterBar, in which case this snippet will help:
#tribe_events_filters_form input[type="submit"]{
width: auto !important;
}
/* or if you want it to still display full width */
#tribe_events_filters_form input[type="submit"] {
margin: auto 0 !important;
}
Hope that helps,
Best,
Nico