diff --git a/README.md b/README.md
index 0260aab..5512992 100644
--- a/README.md
+++ b/README.md
@@ -383,8 +383,8 @@ per theme — a single place to look, unlike the old distro's split:
 | `waybar.jsonc` | whole-swap for the bar *layout* (must be plain JSON) |
 | `rofi.rasi` | **whole-swap**: replaces the generated launcher/menu theme entirely |
 
-Five themes ship a `waybar.css` identity (summer-day, summer-night,
-executive-slate, boreal, neon-glass). Custom user themes can live in
+Four themes ship a `waybar.css` identity (summer-day, summer-night,
+executive-slate, boreal). Custom user themes can live in
 `$NOMARCHY_PATH/themes/` (preset lookup) and `nomarchy.themesDir` (eval-time
 asset probe).
 
diff --git a/agent/BACKLOG.md b/agent/BACKLOG.md
index 28e23b9..dbc299f 100644
--- a/agent/BACKLOG.md
+++ b/agent/BACKLOG.md
@@ -113,12 +113,6 @@ gating. Fix: name-agnostic scan aligned with battery-notify. Cost:
 small multi-file; `[blocked:hw]` only to confirm on non-BAT* hardware —
 logic still ships at V1.
 
-### 62. Optional CI: whole-swap CSS self-containment
-Contrast check does not require that a `waybar.css` defines every
-`@color` it references, nor that every preset has preview + backgrounds.
-A cheap gate would have caught neon-glass. Cost: small tool + flake
-check; V0.
-
 ### 63. Generated Waybar: identity-bar affordances (powermenu + logo)
 Whole-swap bars ship `custom/powermenu` and a left logo → main menu; the
 generated `waybar.nix` bar has neither. Optional parity add for
@@ -238,7 +232,7 @@ _(Generated Waybar missing identity-bar affordances → **#63**.)_
   executive-slate, and the generated style have. Functional OK;
   visual hierarchy weak. Cost: CSS pass; V3.
 
-_(Optional CI: whole-swap CSS self-containment → **#62**.)_
+_(Optional CI: whole-swap CSS self-containment → **#62** ✓ 2026-07-10.)_
 
 ### Per-theme design audit (2026-07-09)
 
diff --git a/agent/JOURNAL.md b/agent/JOURNAL.md
index b662997..c5608bb 100644
--- a/agent/JOURNAL.md
+++ b/agent/JOURNAL.md
@@ -17,6 +17,17 @@ Template:
 
 ---
 
+## 2026-07-10 — #62 whole-swap CSS self-containment CI gate
+- **Task:** NEXT #62 — cheap gate that waybar.css defines every @color it
+  references (would have caught neon-glass) + preview/backgrounds present.
+- **Did:** `tools/check-theme-wholeswap.py` + `checks.theme-wholeswap` in
+  flake.nix. README: five themes → four (drop quarantined neon-glass).
+  Closed #62.
+- **Verified:** **V0** — script OK on themes/ (24 presets, 4 whole-swaps);
+  negative fixture with `@text`/`@base` and zero defines fails as expected;
+  `nix build .#checks.x86_64-linux.theme-wholeswap` green.
+- **Next suggestion:** #59 NVIDIA install comments, or #60 BAT*-agnostic.
+
 ## 2026-07-10 — #61 Review Source line tracks offline/online
 - **Task:** NEXT #61 — Review panel Source must match the cache.nixos.org
   probe (`OFFLINE`), not always claim “no network needed”.
diff --git a/flake.nix b/flake.nix
index e62f530..fc7f225 100644
--- a/flake.nix
+++ b/flake.nix
@@ -155,6 +155,17 @@
               touch $out
             '';
 
+          # Whole-swap waybar.css is read raw (no palette prepend) — every
+          # @color it references must be @define-color'd in the same file
+          # (neon-glass shipped zero defines; BACKLOG #62). Also gate
+          # preview.png + non-empty backgrounds/ per preset.
+          theme-wholeswap = pkgs.runCommand "nomarchy-theme-wholeswap"
+            { nativeBuildInputs = [ pkgs.python3 ]; }
+            ''
+              python3 ${./tools/check-theme-wholeswap.py} ${./themes}
+              touch $out
+            '';
+
           # The README option tables must track the live `nomarchy.*`
           # surface. The surface is walked at eval time from the four
           # option-declaring modules (their lazy `config` halves stay
diff --git a/tools/check-theme-wholeswap.py b/tools/check-theme-wholeswap.py
new file mode 100644
index 0000000..bd72e11
--- /dev/null
+++ b/tools/check-theme-wholeswap.py
@@ -0,0 +1,111 @@
+#!/usr/bin/env python3
+"""Whole-swap theme asset + CSS self-containment (BACKLOG #62).
+
+waybar.nix applies themes/<slug>/waybar.css *raw* — no palette @define-color
+block is prepended. A whole-swap that references @text without defining it
+is broken at apply time (neon-glass, 2026-07-09). This gate fails that class
+of bug before it ships.
+
+Also asserts every themes/*.json has preview.png + non-empty backgrounds/.
+
+Wired as `checks.theme-wholeswap` in flake.nix; runnable directly:
+    python3 tools/check-theme-wholeswap.py themes/
+"""
+from __future__ import annotations
+
+import re
+import sys
+from pathlib import Path
+
+# CSS at-rules that look like @name but are not GTK/CSS color names.
+AT_RULES = frozenset(
+    {
+        "keyframes",
+        "media",
+        "import",
+        "supports",
+        "font-face",
+        "charset",
+        "page",
+        "define-color",
+        "layer",
+        "container",
+        "property",
+        "scope",
+    }
+)
+
+COMMENT_RE = re.compile(r"/\*.*?\*/", re.DOTALL)
+DEFINE_RE = re.compile(r"@define-color\s+([A-Za-z_][\w-]*)")
+# Color uses: @name, alpha(@name, …) — same token shape as defines.
+AT_REF_RE = re.compile(r"@([A-Za-z_][\w-]*)")
+
+
+def strip_comments(css: str) -> str:
+    return COMMENT_RE.sub("", css)
+
+
+def check_waybar_css(path: Path, failures: list[str]) -> None:
+    raw = path.read_text(encoding="utf-8")
+    css = strip_comments(raw)
+    defs = set(DEFINE_RE.findall(css))
+    refs = set(AT_REF_RE.findall(css)) - AT_RULES - defs
+    # define-color lines also match AT_REF_RE for the rule name only via
+    # @define-color — already in AT_RULES. Color names on define lines
+    # appear as the capture of DEFINE_RE only when after define-color;
+    # AT_REF_RE on "@define-color foo" yields "define-color", not "foo".
+    # On "color: @text" yields "text". Good.
+    if refs:
+        missing = ", ".join(sorted(refs))
+        failures.append(f"{path}: undefined color refs: {missing}")
+
+
+def check_assets(themes_dir: Path, failures: list[str]) -> None:
+    jsons = sorted(themes_dir.glob("*.json"))
+    if not jsons:
+        failures.append(f"{themes_dir}: no themes/*.json found")
+        return
+    for jp in jsons:
+        slug = jp.stem
+        tdir = themes_dir / slug
+        preview = tdir / "preview.png"
+        if not preview.is_file():
+            failures.append(f"{slug}: missing {preview.relative_to(themes_dir)}")
+        bg = tdir / "backgrounds"
+        if not bg.is_dir():
+            failures.append(f"{slug}: missing backgrounds/")
+        elif not any(bg.iterdir()):
+            failures.append(f"{slug}: backgrounds/ is empty")
+
+
+def main() -> int:
+    if len(sys.argv) != 2:
+        print(f"usage: {sys.argv[0]} <themes-dir>", file=sys.stderr)
+        return 2
+    themes_dir = Path(sys.argv[1])
+    if not themes_dir.is_dir():
+        print(f"not a directory: {themes_dir}", file=sys.stderr)
+        return 2
+
+    failures: list[str] = []
+    check_assets(themes_dir, failures)
+    for css in sorted(themes_dir.glob("*/waybar.css")):
+        check_waybar_css(css, failures)
+
+    if failures:
+        for f in failures:
+            print(f"theme-wholeswap: {f}", file=sys.stderr)
+        print(f"theme-wholeswap: {len(failures)} failure(s)", file=sys.stderr)
+        return 1
+
+    n_css = len(list(themes_dir.glob("*/waybar.css")))
+    n_json = len(list(themes_dir.glob("*.json")))
+    print(
+        f"theme-wholeswap: ok — {n_json} presets (preview+backgrounds), "
+        f"{n_css} whole-swap waybar.css self-contained"
+    )
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())