unitless size doesn't work size:3

### Description

`<[s:1]>` should be equivalent to `<[s:0.25rem]>`. But it compiles to `width: 1;height:1` which doesn't work for now

### Reproduction

https://scrimba.com/scrim/cG8V82Ty

### System Environment

```text
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Start with the linked Scrimba reproduction and trace how `` is compiled, comparing its generated `width: 1;height:1` with the expected `0.25rem` behavior. Done when unitless size values compile equivalently to the rem-based form and the reproduction shows the correct sizing.

Written by the indexing model from the issue text.