Apply suggestions from code review

Author: Rich-Harris

packages/svelte/messages/compile-warnings/style.md

@@ -2,6 +2,16 @@
 
 > Unused CSS selector "%name%"
 
-Svelte traverses both the template and the `<style>` tag to find out which of the CSS selectors are actually in use. It will prune (i.e. remove) those selectors which appear unused and warn you about it.
+Svelte traverses both the template and the `<style>` tag to find out which of the CSS selectors are not used within the template, so it can remove them.
 
-In some situations Svelte may be too strict and you _know_ that the selector is used. In this case, you can use [`:global` or `:global(...)`](global-styles) to prevent them from being pruned.
+In some situations a selector may target an element that is not 'visible' to the compiler, for example because it is part of an `{@html ...}` tag or you're overriding styles in a child component. In these cases, use [`:global`](/docs/svelte/global-styles) to preserve the selector as-is:
+
+```svelte
+<div class="post">{@html content}</div>
+
+<style>
+  .post :global {
+    p {...}
+  }
+</style>
+```

packages/svelte/messages/server-errors/lifecycle.md

@@ -2,4 +2,4 @@
 
 > `%name%(...)` is not available on the server
 
-Certain methods such as `mount` cannot be invoked while running in a server context. Avoid calling them eagerly, i.e. not during the server render.
+Certain methods such as `mount` cannot be invoked while running in a server context. Avoid calling them eagerly, i.e. not during render.