diff --git a/.github/workflows/csstolua.lua b/.github/workflows/csstolua.lua
new file mode 100644
index 00000000..ace8a03b
--- /dev/null
+++ b/.github/workflows/csstolua.lua
@@ -0,0 +1,116 @@
+local res = {}
+
+local function is_valid_ident(ident)
+  local keyword = {
+    ['do'] = true,
+    ['end'] = true,
+    ['if'] = true,
+    ['then'] = true,
+    ['local'] = true,
+    ['function'] = true,
+    ['return'] = true,
+    ['while'] = true,
+    ['repeat'] = true,
+    ['until'] = true,
+    ['for'] = true,
+    ['in'] = true,
+    ['true'] = true,
+    ['false'] = true,
+    ['nil'] = true,
+  }
+  if type(ident) ~= 'string' or keyword[ident] then
+    return false
+  end
+  return ident:find('^[_%a][_%w]*$') ~= nil
+end
+
+local function set(cssvar, v)
+  local before, after = cssvar:match('^(.+)%-+(.+)$')
+  if not after then
+    res[tonumber(cssvar) or cssvar] = v
+    return
+  end
+
+  after = tonumber(after) or after
+  local cur = res
+  for k in before:gmatch('[^%-_]+') do
+    k = tonumber(k) or k
+    cur[k] = cur[k] or {}
+    cur = cur[k]
+  end
+
+  if type(cur[after]) == 'table' then
+    cur, after = cur[after], 'default'
+  end
+  assert(cur[after] == nil or cur[after] == v)
+  cur[after] = v
+end
+
+local function print_recur(value, _ind)
+  _ind = _ind or 0
+
+  if type(value) == 'table' then
+    io.write('m {')
+    _ind = _ind + 2
+
+    for k, v in pairs(value) do
+      local fmt = is_valid_ident(k) and '%s = ' or '[%q] = '
+      io.write(('\n%s' .. fmt):format((' '):rep(_ind), k))
+      print_recur(v, _ind)
+      io.write(',')
+    end
+
+    _ind = _ind - 2
+    io.write(('\n%s}'):format((' '):rep(_ind)))
+  else
+    io.write(('%q'):format(value))
+  end
+end
+
+local defs = {}
+for ln in io.lines() do
+  local k, v = ln:match('^%s*%-%-(%w.-)%s*:%s*(.-)%s*;%s*$')
+  if k then
+    table.insert(defs, { k, v })
+  end
+end
+
+-- Since we are un-flattening, ensure that longer keys (whose prefix could
+-- match another key) are visited first.
+table.sort(defs, function(a, b)
+  return a[1] > b[1]
+end)
+
+for _, kv in ipairs(defs) do
+  set(unpack(kv))
+end
+
+assert(res.scale == nil)
+res.scale = {}
+for color, scale in pairs(res.base.color) do
+  if type(scale) == 'table' then
+    res.scale[color] = {}
+    for i, v in pairs(scale) do
+      res.scale[color][i + 1] = v
+    end
+  else
+    res.scale[color] = scale
+  end
+end
+
+io.write([=[
+local mt = {
+  __index = function(_, k)
+    error('invalid index: ' .. k)
+  end,
+}
+---@generic T
+---@param tbl T
+---@return T
+local function m(tbl)
+  return setmetatable(tbl, mt)
+end
+local M = ]=])
+
+print_recur(res)
+io.write('\n')
diff --git a/.github/workflows/update-color-primitives.yml b/.github/workflows/update-color-primitives.yml
index f63831d5..59fd7e52 100644
--- a/.github/workflows/update-color-primitives.yml
+++ b/.github/workflows/update-color-primitives.yml
@@ -2,18 +2,19 @@ name: Get/Update Primer Color Primitives
 
 env:
   _DEST_DIR: "${{ github.workspace }}/lua/github-theme/palette/primitives"
-  _JSON_DIR: "${{ github.workspace }}/node_modules/@primer/primitives/dist/json/colors"
+  _SRC_DIR: "${{ github.workspace }}/node_modules/@primer/primitives/dist/internalCss"
   _LICENSE_GLOB: "${{ github.workspace }}/node_modules/@primer/primitives/[Ll][Ii][Cc][Ee][Nn][Ss][Ee]*"
   _PRIMITIVES_PKGJSON: "${{ github.workspace }}/node_modules/@primer/primitives/package.json"
+  _CSSTOLUA: "${{ github.workspace }}/.github/workflows/csstolua.lua"
 
 on:
   workflow_dispatch:
   schedule:
-    # 3x per week (every other day) at 12:40pm Pacific Time
-    - cron: "40 19 * * 1,3,5"
+    # once a week, every Monday at 12:40pm Pacific Time
+    - cron: "40 19 * * 1"
 
 jobs:
-  get-colors:
+  install-primitives:
     runs-on: ubuntu-latest
     permissions:
       checks: write
@@ -25,6 +26,9 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+      - uses: rhysd/action-setup-vim@v1
+        with:
+          neovim: true
 
       - uses: actions/setup-node@v4
         with:
@@ -34,21 +38,22 @@ jobs:
       - run: npm i @primer/primitives@latest
 
       - run: |
-          set -u +f
+          set -eu +f
           shopt -s nocaseglob failglob
           license="$(<$_LICENSE_GLOB)"
           rm -r "$_DEST_DIR" || :
           mkdir -p "$_DEST_DIR"
-          cd "$_JSON_DIR"
+          cd "$_SRC_DIR"
 
           if jq -e .version "$_PRIMITIVES_PKGJSON"; then
             version="M._VERSION = vim.json.decode([=[$(jq -e .version "$_PRIMITIVES_PKGJSON")]=], { luanil = { object = false, array = false } })"
           fi
 
-          for file in *.json; do
-            cat >|"${_DEST_DIR}/${file%.json}.lua" <<EOF
+          for file in *.css; do
+            values="$(nvim -l "$_CSSTOLUA" < "$file")"
+            cat >| "${_DEST_DIR}/${file%.css}.lua" <<EOF
           -- NOTE: THIS IS AN AUTO-GENERATED FILE. DO NOT EDIT BY-HAND.
-          local M = vim.json.decode([=[$(<"$file")]=], { luanil = { object = false, array = false } })
+          ${values}
           ${version-}
           M._LICENSE = [=[
           $license]=]