Syntax Highlighting

So far we’ve styled the VS Code UI. Now let’s colour the actual code.

Token Colours

VS Code uses TextMate scopes to identify parts of your code — keywords, strings, comments, function names, and so on. You style them with tokenColors entries, each containing a name, scope, and settings.

Add a tokenColors section inside theme:

theme:
  tokenColors:
    - name: Comments
      scope: comment
      settings:
        foreground: $(std.fg.inactive)
        fontStyle: italic

    - name: Keywords
      scope: keyword, storage.type
      settings:
        foreground: $(accent)

    - name: Strings
      scope: string
      settings:
        foreground: $(colors.green)

    - name: Numbers
      scope: constant.numeric
      settings:
        foreground: $(colors.yellow)

    - name: Functions
      scope: entity.name.function
      settings:
        foreground: $(colors.cyan)

    - name: Classes
      scope: entity.name.class, entity.name.type
      settings:
        foreground: $(colors.blue)
        fontStyle: bold

How Scopes Work

Each scope is a TextMate grammar selector. VS Code matches them against the tokens in your code:

• comment matches all comments
• keyword matches if, return, import, etc.
• string matches string literals
• entity.name.function matches function declarations

Comma-separated scopes (like keyword, storage.type) apply the same style to multiple scopes. VS Code uses the first matching rule, so order can matter for overlapping scopes.

The settings block supports:

• foreground — the text colour
• fontStyle — italic, bold, underline, or combinations like bold italic

Build It

npx @gesslar/sassy build ocean.yaml

To see the result, install the theme in VS Code and open a source file. Comments should appear faded and italic, keywords in your accent colour, strings in green, and so on.

Tip

Use VS Code’s Developer: Inspect Editor Tokens and Scopes command (from the Command Palette) to see exactly which scopes apply to any token in your code. This is invaluable when fine-tuning syntax highlighting.

Semantic Token Colours

VS Code also supports semantic tokens — language-aware tokens provided by language servers rather than TextMate grammars. These are more precise: a language server knows the difference between a variable declaration and a variable reference, for example.

You style them with semanticTokenColors. Each key is a semantic token selector, and values can be either a string (shorthand for foreground) or an object with foreground and/or fontStyle:

theme:
  semanticTokenColors:
    variable.declaration:
      foreground: $(std.fg)
      fontStyle: italic
    function.declaration:
      foreground: $(accent)
      fontStyle: bold
    "string:escape": $$yellow

Tip

Semantic tokens override tokenColors when a language server is active. Use tokenColors as the baseline and semanticTokenColors for precision where it matters.

The theme is starting to look real. Let’s finish it off with UI polish.