[docs] clarify css option (#7271)

site/content/docs/04-compile-time.md

@@ -73,7 +73,7 @@ The following options can be passed to the compiler. None are required:
 | `accessors` | `false` | If `true`, getters and setters will be created for the component's props. If `false`, they will only be created for readonly exported values (i.e. those declared with `const`, `class` and `function`). If compiling with `customElement: true` this option defaults to `true`.
 | `customElement` | `false` | If `true`, tells the compiler to generate a custom element constructor instead of a regular Svelte component.
 | `tag` | `null` | A `string` that tells Svelte what tag name to register the custom element with. It must be a lowercase alphanumeric string with at least one hyphen, e.g. `"my-element"`.
-| `css` | `true` | If `true`, styles will be included in the JavaScript class and injected at runtime. It's recommended that you set this to `false` and use the CSS that is statically generated, as it will result in smaller JavaScript bundles and better performance.
+| `css` | `true` | If `true`, styles will be included in the JavaScript class and injected at runtime for the components actually rendered. If `false`, the CSS will be returned in the `css` field of the compilation result. Most Svelte bundler plugins will set this to `false` and use the CSS that is statically generated for better performance, as it will result in smaller JavaScript bundles and the output can be served as cacheable `.css` files.
 | `cssHash` | See right | A function that takes a `{ hash, css, name, filename }` argument and returns the string that is used as a classname for scoped CSS. It defaults to returning `svelte-${hash(css)}`
 | `loopGuardTimeout` | 0 | A `number` that tells Svelte to break the loop if it blocks the thread for more than `loopGuardTimeout` ms. This is useful to prevent infinite loops. **Only available when `dev: true`**
 | `preserveComments` | `false` | If `true`, your HTML comments will be preserved during server-side rendering. By default, they are stripped out.