diff --git a/docs/MIGRATION_PLAYBOOK.md b/docs/MIGRATION_PLAYBOOK.md
index 786fc11..6399137 100644
--- a/docs/MIGRATION_PLAYBOOK.md
+++ b/docs/MIGRATION_PLAYBOOK.md
@@ -57,6 +57,26 @@
 - Playwright probe → pageerrors empty.
 - **Cleanup dead videojs CSS** — `.video-js`, `.vjs-*`, `@keyframes vjs-*`, `.waiting .loading-spinner` rules **видалити** з `views/static/css/index.css` + `views/css/css_<page>.etlua` (для video page) AFTER player migrated. Залишити **тільки** якщо site has окремі pages що ще videojs (embed.etlua, id_xvideos.etlua module — conditional render). Не видалити `views/static/css/video-js.css` файл (used by embed iframe).
 
+#### Flat-site CSS override (P.flat) — discovered 2026-05-05 (gocc4 batch set B)
+
+**Trigger:** site has FLAT theme — single limiter div з `padding:56.25% 0 0` aspect-ratio trick (single-level structure, не 2-level wrapper>player).
+
+Examples discovered: `.fplayer` (8155), `.bloque-video-vid` (8156), `.vid-blck-vid` (8162), `.vbrlmtr` (8150).
+
+**Symptom:** після PlayerJS DOM replace — `pjs_container` виштовхується padding-trick poза visible area → ad-test fails (asg-container injection не fires bo no click target).
+
+**Fix:** додати inline `<style>` у `id_index.etlua` перед PlayerJS DOM:
+```css
+.<lmtr-class>{padding:0!important;aspect-ratio:16/9;overflow:visible}
+.<lmtr-class> #pjs_container{position:absolute;top:0;left:0;width:100%;height:100%}
+```
+
+Replace `<lmtr-class>` на site-native limiter (e.g. `.fplayer`).
+
+**Detection cue:** після initial Branch P attempt → ad-test fail check #5 (`.asg-container injected on click`). Якщо це так — apply P.flat fix + retry ad-test.
+
+**Альтернативно:** ці sites мають **2-level theme** (outer plain wrapper + inner player block, e.g. `.video-card-limiter > .video-player` у 8154) → straightforward replace, no override needed.
+
 ### Branch S (Spot ID rotation) — якщо A2=yes
 
 - Replace IDs у `views/static/js/ad-config.js` (popunder.spot, vast.spot).