Image quality issues

Microsoft

I'd like to use custom icons in various places on my Communications site, but I'm having trouble getting them to display well. These are images created in a vector-based illustration program.  For instance, I'm trying to use custom images in the Quick Links web part and some of the images are cut off, some are just poor quality when displayed, etc. What specifications should I adhere to when creating illustrations for use in SharePoint Online?

2 Replies
What are the formats of these pictures?

They're .png.