Left, right... positioning do not get space from theme

[theo-mesnil]

🐛 Bug Report

When i add a left, right... on a box with system positioning, i can't get the space from theme.

To Reproduce

const Box = styled.div`
 ${positioning};
`

<Box position="absolute" left="sm" top="sm" />

Expected behavior

Get the space.sm from theme.

## System:
 - OS: macOS 10.15.3
 - CPU: (8) x64 Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
 - Memory: 48.82 MB / 8.00 GB
 - Shell: 3.2.57 - /bin/bash
## Binaries:
 - Node: 12.4.0 - ~/.asdf/installs/nodejs/12.4.0/bin/node
 - Yarn: 1.19.1 - ~/.asdf/installs/nodejs/12.4.0/.npm/bin/yarn
 - npm: 6.9.0 - ~/.asdf/installs/nodejs/12.4.0/bin/npm
 - Watchman: 4.9.0 - /usr/local/bin/watchman
## npmPackages:
 - @xstyled/styled-components: ^1.15.1 => 1.15.1 
 - @xstyled/system: ^1.15.1 => 1.15.1 
 - styled-components: ^4.0.0 || ^5.0.0 => 5.0.0 

[gregberge]

It is not the bug, it is the behaviour. I plan to change it but it is a breaking change since all existing positioning (top, right, bottom, left) could break.

[gregberge]

Fixed in v2, inset is a new section in theme to use for top, left, right, bottom.