When building themes, it’s often worthwhile to consider how your theme can compose with others.
In some cases you might want to break your theme into modular parts, like
Since themes are still early, we recommend getting started by building themes that are more monolithic. It’s less overhead to get started and a theme can always be broken up into smaller themes later.
In Gatsby themes you can apply global layouts by using
wrapPageElement. For better theme
composition it’s recommended to use this feature sparingly. It’s a great fit for setting up any
necessary React Context providers. You shouldn’t typically
add any layout components, such as headers or footers, because it will be applied globally which
could cause issues with other themes.
Read more on layouts and Gatsby Themes