Update source/import-css/index.html.md.erb

Co-authored-by: Romaric Pascal <romaric.pascal@digital.cabinet-office.gov.uk>

Author: seaemsi

source/import-css/index.html.md.erb

@@ -117,7 +117,7 @@ For example, to import the button component, add the following to your Sass file
 ```scss
 @import "node_modules/govuk-frontend/dist/govuk/components/button";
 ```
-We're deprecating using _<COMPONENT_NAME>.scss files (like node_modules/govuk-frontend/dist/govuk/components/button/button) and will remove them in the next major release of GOV.UK Frontend.
+We're deprecating using `_<COMPONENT_NAME>.scss` files (like `node_modules/govuk-frontend/dist/govuk/components/button/button`) and will remove them in the next major release of GOV.UK Frontend.
 
 ## Simplify Sass import paths