• Improved performance of core module
• Splits core module and style functions into separate packages for smaller bundling options
• Uses microbundle for main styled-system package
• New custom styles API
• Mostly backwards compatible with v4
• Uses theme.sizes scale for width, height, minWidth, minHeight, maxWidth, maxHeight, and size props

Breaking

• Removes propTypes from core (an optional package will be provided)
• Moves themeGet to a separate package @styled-system/theme-get
• No longer converts numbers to strings with px unit (most CSS-in-JS libraries now handle this)
• Removes these utilities: isObject, is, px, num, createMediaQuery, defaultBreakpoints, merge, cloneFunction, mapProps
• No longer returns null for empty values (now returns {})
• Replaces width and height theme scales with theme.sizes

To do

• Update docs Update docs for V5 #521
• Update should-forward-prop implementation Update should-forward-prop package for V5 #522
• Add prop-types package
• Split up style packages

Fixes #475
Fixes #444