How to set slide width in virtual mode?

[zhaozhemin]

Normally, you can set slide width by writing CSS, e.g. .swiper-slide { width: 80% }, when slidesPerView is auto. But virtual: true cannot be used with slidesPerView: auto. If I override the width with !important using CSS, the width is right but the transform etc., is all wrong.

[danilosimonatto]

You can't use slidesPerView in auto because as stated in #2287 virtual slides must know the slide size before it is rendered.