Not all aspects of the CSS Grid spec are supported

```css
/* works */
.main {
grid-column: 2 / 3;
}

/* Error: Unsupported property error: grid-column is not a supported property */
.main {
grid-column: 2 / span 3;
}
```

Named areas don't work either, taking away a lot of the nicer aspects of CSS grids.

Start by locating the implementation and tests for CSS Grid property parsing, then reproduce the two grid-column examples from the issue. Investigate support for the span form and named areas; done means these documented CSS Grid cases are accepted without the reported unsupported-property error.

Written by the indexing model from the issue text.