feat: minor style updates, use svg markers

• minor style updates inside the infobox (use sans-serif font, remove top margin, allow scrolling of content inside infobox)
• use svg markers
• optimize svg images for size
• fix typo
• use <button> for infobox close element as it's semantically better

Also, i bought the domain matekate.de and redirected it to your deployment. Thanks for your work. I love it!