✏️ Fix headings

docs/src/developer_documentation/custom_themes.md

@@ -6,7 +6,7 @@ Themes consist of two different parts, the theme itself, and its corresponding c
 
 The theme is just a dictionary containing functions. These functions specify how the entries and cover should look, as well as global rules for the whole document. We'll cover the required structure of this variable in a [later](#the-theme-variable) section.
 
-Components are simply functions stored in a module. These functions contain things like pro/con tables and decision-matrices. Most components are just standalone, but the Notebookinator does supply some utility functions to help with implementing harder components. Implementing components will be covered in [this](#writing-components) section.
+Components are simply functions stored in a module. These functions contain things like pro/con tables and decision matrices. Most components are just standalone, but the Notebookinator does supply some utility functions to help with implementing harder components. Implementing components will be covered in [this](#writing-components) section.
 
 ## File Structure
 
@@ -62,7 +62,7 @@ The `ctx` argument provides context about the current entry being created. This
 
 We'll write these functions in the `foo/entries.typ` file. Below are some minimal starting examples:
 
-### Frontmatter
+#### Frontmatter
 
 ```typ
 // foo/entries.typ
@@ -77,7 +77,7 @@ We'll write these functions in the `foo/entries.typ` file. Below are some minima
 }
 ```
 
-### Body
+#### Body
 
 ```typ
 // foo/entries.typ
@@ -92,7 +92,7 @@ We'll write these functions in the `foo/entries.typ` file. Below are some minima
 }
 ```
 
-### Appendix
+#### Appendix
 
 ```typ
 // foo/entries.typ