How to make vector graphics sharp on web?

Hi

I have this problem, that every time I make a vector-picture and upload it to my CMS, then its not really razor sharp but more a kind of blurry on the edges. Why is that, and what can I do to fix it?

I do export it for web, choose PNG and I know, that a website on a screen is pixels, but I still think it should be possible to have a more sharp picture.

Heidi