Authoring Cate Themes

A Cate theme is ONE JSON object that styles the whole IDE:

• app — the window/panel chrome (CSS custom properties: surfaces, text, borders, accents)
• terminal — the xterm palette (background/foreground + the 16 ANSI colors)
• editor — the Monaco code editor (base + syntax token colors)

There is no separate terminal theme any more — one theme colors everything.

The canonical machine-readable schema is theme.schema.json in this skill folder. Validate every theme against it before saving.

Where themes live

User themes are stored in Cate's settings file under the customThemes array, and the active theme is activeThemeId:

macOS:   ~/Library/Application Support/cate/config.json
Linux:   ~/.config/cate/config.json
Windows: %APPDATA%/cate/config.json

Schema

{
  "version": 1,
  "id": "midnight-ember",        // REQUIRED, unique kebab-case slug
  "name": "Midnight Ember",      // REQUIRED, display name
  "type": "dark",                // REQUIRED: "dark" | "light" (drives system light/dark auto-switch + editor base)
  "author": "You",               // optional
  "bootBackground": "#1a1714",   // optional — exact cold-launch window bg (defaults to surface-0)

  "app": {                       // app chrome — see "App colors" below. PARTIAL: omitted keys inherit the base.
    "surface-0": "#1a1714",
    "surface-1": "#221d18",
    "text-primary": "#e7ddd0",
    "text-muted": "#9b9186",
    "border-focus": "#e0683c",
    "focus-blue": "#e0683c",
    "agent-rgb": "224 104 60"
  },

  "terminal": {                  // REQUIRED full xterm palette — ordinary shell output
    "background": "#1a1714", "foreground": "#e7ddd0", "cursor": "#e0683c",
    "selectionBackground": "#3a2f26",
    "black": "#1a1714", "red": "#e0683c", "green": "#8fa86a", "yellow": "#d9a441",
    "blue": "#5f90c4", "magenta": "#b06aa0", "cyan": "#5fa8a8", "white": "#d8cdbf",
    "brightBlack": "#6b6258", "brightRed": "#f0855a", "brightGreen": "#a6c47f",
    "brightYellow": "#e8bd6a", "brightBlue": "#7aa8d6", "brightMagenta": "#c884b8",
    "brightCyan": "#7cc0c0", "brightWhite": "#f4ece1"
  },

  "editor": {                    // REQUIRED Monaco syntax
    "base": "vs-dark",           // "vs" for light themes, "vs-dark" for dark
    "tokens": [                  // syntax rules — foreground is hex WITHOUT the leading #
      { "token": "comment", "foreground": "6b6258", "fontStyle": "italic" },
      { "token": "keyword", "foreground": "e0683c" },
      { "token": "string",  "foreground": "8fa86a" },
      { "token": "constant.numeric", "foreground": "d9a441" },
      { "token": "type",    "foreground": "5f90c4" },
      { "token": "entity.name.function", "foreground": "b06aa0" }
    ],
    "colors": {                  // optional Monaco IColors (# prefixed)
      "editor.background": "#1a1714",
      "editor.foreground": "#e7ddd0"
    }
  }
}

App colors (keys under app)

All optional — anything you omit inherits the base for the theme's type. surface-0..6 (layered backgrounds, 0 = base), titlebar-bg, canvas-bg, canvas-bg-alt, canvas-backdrop-scrim, grid-dot, grid-line, border-subtle, border-strong, border-focus, text-primary, text-secondary, text-muted, text-inverse, focus-blue, activity-green, activity-orange, shadow-node, shadow-node-focused, node-bg-active, node-dim-overlay, scrollbar-thumb, scrollbar-thumb-hover, surface-hover, surface-hover-strong, git-added, git-modified, git-deleted, git-untracked, git-renamed, panel-terminal, panel-browser, panel-editor, panel-canvas, agent-rgb, agent-light-rgb.

Values are hex (#rrggbb / #rrggbbaa), rgba(...), or — for agent-rgb / agent-light-rgb only — three space-separated channels like "224 104 60".

Color & accessibility guidance

• Body text on surface must hit WCAG AA: contrast ratio ≥ 4.5:1 (text-primary on surface-1). Compute it; don't eyeball it.
• Every ANSI color must be legible on terminal.background. The usual failures: blue and brightBlack on dark backgrounds, yellow/white on light backgrounds.
• Keep red and green clearly distinct — diff and test output depend on it.
• border-focus / focus-blue must stand out against surface-1 (focus rings, selection).
• For light themes set "type": "light" and "editor": { "base": "vs" }.

Validate before saving

1. Parse your JSON.
2. Check it against theme.schema.json. If ajv is available: npx ajv validate -s theme.schema.json -d mytheme.json. Otherwise verify: all required keys present; every color matches ^#?[0-9a-fA-F]{6,8}$ (Monaco tokens[].foreground has NO #, everything else DOES); type is dark|light.
3. Run the contrast checks above.

Apply it — two ways

Preferred — import via Settings (validated by the app, no file surgery): Save the theme as <name>.cate-theme.json and tell the user: "Open Settings → Appearance → Import…, then pick this file." Then select it in the theme catalog.

Direct — append to config.json (only if asked to apply without the UI):

1. Read <userData>/config.json (paths above). If it doesn't parse, STOP.
2. Append your validated theme to the customThemes array (create it if absent). Ensure id is unique within that array.
3. To make it active now, set activeThemeId to your theme's id.
4. NEVER reorder or overwrite existing customThemes, and never touch unrelated keys. Changes apply on next launch or when settings are re-read.

See examples/ for a complete dark and light theme to copy from.