I am trying to add a css file to the front page only in drupal 8.
I have seen the documentation:

 - https://www.drupal.org/theme-guide/8/assets

I just need to know the HOOK machine name for front page:

` function THEMENAME_preprocess_HOOK(&$variables) {
 $variables['#attached']['library'][] = 'CSSPATH';
}`


Thanks!