Using $parent-selector variable doesn't fully restrict styles to specified selector.

[dev-willis]

Describe the issue

There seem to be styles that do not have the value of $parent-selector prepended to them. E.g., box-sizing: border-box; is being applied to everything rather than just those elements that are descendants of the parent selector.

Current Behavior

Some elements outside the parent selector are altered by PicoCSS styles.

Expected Behavior

All PicoCSS styles should be applied within the parent selector only.