Swipe - enhance style of swiper

[nadja_swiss_parks]

The icon for the slider should be much smaller. Currently, too much of the images are hidden, especially on mobile devices, see attachement.

Propositions:

- if a circle around the triangles is shown, the circle should be semi-transparent (mobile & desktop)

- only the triangles (light with a dark border) could be shown without a circle (mobile & desktop)

- the triangles could be smaller on mobile devices

- the vertical line separating the two images could be thinner on mobile devices