Merge pull request #157 from oddbird/add-host-caveats-to-caveats-section

add :host caveats to caveats section

README.md

@@ -123,6 +123,13 @@ some caveats which will need accommodations:
     `shadowRoot`). You'll need to manually inject the styles yourself with
     `injectStyles(myShadow)`.
 
+  - As a stylesheet is injected into the main document, if your host element is
+    a popover, styling with `:host` gets tricky beause `:host` styles always
+    take lower precedence than the main document styles. This is a limitation
+    of CSS and there's not a reasonable workaround. The best workaround for
+    now is to add `!important` to conflicting properties in your `:host` rule.
+    See [#147](https://github.com/oddbird/popover-polyfill/issues/147) for more.
+
 ## Contributing
 
 Visit our [contribution guidelines](https://github.com/oddbird/popover-polyfill/blob/main/CONTRIBUTING.md).