Suggestions for the Next Update

I've been thinking a lot about Open Props and how we can make it better. After building numerous components with Open Props, here are some suggestions for the next update:

**Add:**
- `font-size: 0.875rem | 14px` (Frequently used by designers, especially for links and buttons).
- `border-radius: 4px`.
- `border-radius: 8px`.

**More:**
- Fluid font size.
- Fluid size.
- Gradients (especially multi-layer gradients).
- SVG filters.

I understand that you can create your own props on top of Open Props, but when you encounter certain props frequently with different designs, I think it's time for these props to be included by default.

The issue names no files, tests, or entry points. Review the existing Open Props custom-property definitions and decide which suggestions have an agreed scope; this is done when the selected font sizes, radii, fluid values, gradients, or SVG filters are specified and implemented with corresponding validation.

Written by the indexing model from the issue text.