Default frontmatter

defaults in the headmatter holds frontmatter that every slide starts from. A slide's own keys win.

---
title: My talk
defaults:
  layout: center
  transition: fade
---

Here every slide that does not set layout is centred, including the first one. When the first slide should still be a cover, set layout: cover on it.

Merging with imports

When a slide imports others with src:, the keys on the importing slide win over the keys of the imported slides. In the example below the imported slides get class: from-here:

---
src: ./pages/intro.md
class: from-here
---

A theme can also bring defaults. The deck's own headmatter wins over the theme's, and defaults, fonts, drawings, htmlAttrs and themeConfig are merged key by key. See Themes and addons.