Update addon-types.mdx

docs/addons/addon-types.mdx

@@ -39,7 +39,7 @@ Use this boilerplate code to add a new `button` to Storybook's Toolbar:
 <Callout variant="info">
   The `match` property allows you to conditionally render your toolbar addon, [based on the current view](./writing-addons.md#conditionally-render-the-addon).
 
-  <hr style="margin: -0.75em 0 0.75em" />
+  <hr style={{margin: "-0.75em 0 0.75em"}} />
 
   The `icon` element used in the example loads the icons from the `@storybook/components` package. See [here](../faq.md#what-icons-are-available-for-my-toolbar-or-my-addon) for the list of available icons that you can use.
 </Callout>