Fractional keys in the theme are not working

[herkulano]

🐛 Bug Report

I'm trying to use fractional numbers, like 0.5, for the keys in the theme, as is provided in the default template and it doesn't work.

Code

Implementation

const theme = {
  space: {
    3.5: "6rem",
    4.5: "6rem"
  },
  sizes: {
    6.5: "6rem"
  }
};

const StyledBox = styled.div`
  margin: "4.5 3.5";
  padding: "4.5 3.5";
  width: "6.5";
  height: "6.5";
`;

Result

    margin: "4.5 3.5";
    padding: "4.5 3.5";
    width: "6.5";
    height: "6.5";

Expected

    margin: "6rem 6rem";
    padding: "6rem 6rem";
    width: "6rem";
    height: "6rem";

Working example

https://codesandbox.io/s/sad-mendel-6rt4xp?file=/src/App.js

[herkulano]

Duplicate of https://github.com/styled-components/xstyled/issues/294