Fluid sizes should offer alternatives to the physical viewport units

For the sizes vi or dvi is better than vw

```
--size-fluid-1: clamp(.5rem, 1vw, 1rem);
```

Then we have the vertical horizontal problem. Perhaps I want to size for block-size instead.

Start by locating the fluid size custom properties represented by --size-fluid-1 and review how they currently use vw. Compare the proposed vi, dvi, and block-size alternatives, then clarify which variants and naming should be supported. Done means the project has an agreed, consistent set of fluid sizing alternatives.

Written by the indexing model from the issue text.