build(deps): bump theme-ui from 0.15.7 to 0.16.0

Bumps [theme-ui](https://github.com/system-ui/theme-ui) from 0.15.7 to 0.16.0.
- [Release notes](https://github.com/system-ui/theme-ui/releases)
- [Changelog](https://github.com/system-ui/theme-ui/blob/v0.16.0/CHANGELOG.md)
- [Commits](system-ui/theme-ui@v0.15.7...v0.16.0)

---
updated-dependencies:
- dependency-name: theme-ui
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

packages/app/package.json

@@ -51,7 +51,7 @@
     "react-select": "~5.7.0",
     "react-tabs": "~6.0.0",
     "styled-components": "~5.3.6",
-    "theme-ui": "~0.15.4",
+    "theme-ui": "~0.16.0",
     "throttle-debounce": "~5.0.0",
     "tickedoff": "~1.0.2"
   },