New Olivero theme is a great new front theme introduced with Drupal 9.1. But for now Olivero is not yet stable. Still, here is a simple article to create a sub theme for Olivero.
theming
Building enough Drupal 8 websites I ended up applying always the same basic set of code in my Bootstrap sub theme. Preprocess hooks are a common way in Drupal to add or manipulate variables that you can use in your Twig templates files. Suggestions hooks is a common way in Drupal 8 to extend the templates you can use for any part of your code. Here is a snippet of this, copy this in your theme...
Drupal 7 uses PhpTemplate as theme engine. The system is simple, each module implements its theme functions (HOOK_theme) to generate a markup, in most cases HTML, in a direct way or using a template file (XXXXX.tpl.php). The function of the theme also permits to the module to set variables which, after processing will be used in HTML display. These are 2 options for this theme function Either the...