Layouts provide an easy way to apply styles to multiple pages without having to repeat code.
Create a .astro file under the layouts folder. The <slot /> element refers to the content from the page that uses this layout.
In a page's frontmatter, link the layout property to the layout you want to use. For example:
---
layout: "@layouts/default.astro"
---See https://docs.astro.build/en/core-concepts/layouts/ for more information.