IE11での動作時には、'Symbol' is undefinedエラーが表示されるのでpolyfillが必要です。
npm install --save-dev @babel/polyfill
It should be as simple as including import "@babel/polyfill"
at the top of index.js
Gestalt Docs Broken for IE11 (Windows 8.1) · Issue #197 · pinterest/gestalt