What are vendor prefixes and are they still necessary?

Vendor prefixes are engine-specific prefixes on property names that browsers used for experimental CSS, and today they are rarely needed. Each engine had its own:

• -webkit- for Chrome, Safari and newer Edge
• -moz- for Firefox
• -ms- for Internet Explorer and Edge before Chromium
• -o- for old Opera

.element {
  -webkit-transform: rotate(45deg); /* Safari/Chrome */
  -moz-transform: rotate(45deg);    /* Firefox */
  -ms-transform: rotate(45deg);     /* IE */
  transform: rotate(45deg);         /* Standard */
}

The standard declaration goes last, so any browser that supports it uses it.

Browsers now ship experimental features behind flags instead, and modern CSS features need fewer prefixes. A few properties still require one, such as -webkit-line-clamp. Use a tool like Autoprefixer to add prefixes automatically, only where your supported browsers need them.