Olivero is the default front end theme in Drupal core since version 9.4. It was designed as a modern, accessible, and visually clean alternative to the older Bartik theme.
Named after community member Rachel Olivero, the theme emphasises accessibility and responsive design. It uses modern CSS, supports WCAG 2.1 AA standards, and works beautifully on mobile devices.
Most developers use Olivero as either an evaluation theme when first exploring Drupal, or as a base theme for custom projects. Its code is clean and well structured, which makes it a good reference for learning how modern Drupal themes are built. For production sites, teams usually build a custom theme tailored to their brand, but Olivero proves that out of the box Drupal can look modern and polished without any additional work.