diff --git a/README.md b/README.md
index 4c95192..680998d 100644
--- a/README.md
+++ b/README.md
@@ -1,43 +1,51 @@
 # Animated Background
 
-A browser-based animated desktop background: a WebGL flight scene over
-real terrain, driven by the real sun, moon, stars, and live weather.
+A browser-based animated desktop background: a WebGL flight scene over real
+terrain, driven by the real sun, moon, stars and live weather. Designed to be
+dropped into an iframe or kiosk browser and left running.
 
 ## Features
 
-- **WebGL flight scene** (`vendor/clouds3d.js`): raymarched cloud deck,
-  3D terrain mesh from real elevation data (Copernicus DEM), satellite
-  or street basemap, figure-eight flight path around the configured
-  location with a vertical bob between **15 and 35 km** flight altitude.
-- **Real day/night cycle** driven by the actual sun and moon position
-  (SunCalc) for the configured latitude/longitude — or an accelerated
-  24 h simulation (`CONFIG.day`) for wall-decoration purposes.
-- **Realistic night sky**: ~8700 stars from the Yale Bright Star
-  Catalogue (crisp GL points, size by magnitude, colour by temperature),
-  rotated with the sidereal rate for the site's latitude, plus a Milky
-  Way band and a phase-correct moon.
-- **Aircraft**: low-poly jets (CC0 model) cruising the region on curved
-  routes between real airfields, rolling a random destination at every
-  take-off - sun-lit silhouettes with contrails by day, strobing position
-  lights by night (all parameters in `CONFIG.flights`).
-- **Night lights**: animated car lights along the real motorway/road
-  network and pale-yellow settlement lights (OSM place nodes; bigger
-  towns get more and brighter dots), optionally a NASA VIIRS night-lights
-  satellite overlay. All faded in from dusk, density shaped by a
-  rush-hour curve.
-- **Live weather** (Open-Meteo): current conditions + 4-day forecast
-  widget; the weather code selects the scene's cloud density and colour
-  mood (sunny / cloudy / stormy / night).
-- **Fully cached, offline-capable**: basemap tiles, elevation grid,
-  Overpass road/place data, star catalogue and the last weather payload
-  live permanently in IndexedDB. Once warm, the scene renders fully offline, and a 15-minute cycle transparently retries anything that previously failed. Merged road chains and the decoded settlement list are cached as well and only recomputed when an Overpass cell is actually re-fetched.tiles.expireDays`) can refresh
-  basemap tiles periodically.
-- **Location-aware**: set `CONFIG.location.lat/lon`; everything
-  (flight anchor, terrain tiles, sun/moon, weather, star rotation) is
-  computed from it. If the location is omitted, browser geolocation is
-  tried, falling back to the built-in default (London).
-- Units (°C/°F), six UI languages, CSS-swappable colour themes
-  (Ash/Gruvbox/Nord), configurable clock format, optional debug panel.
+- **WebGL flight scene** (`vendor/clouds3d.js`): a 3D terrain mesh built from
+  real elevation data (Copernicus DEM), a raymarched volumetric cloud deck,
+  and a figure-eight flight path around the configured location with a
+  vertical bob inside the 15-35 km flight band.
+- **One physical light model** shared by sky, clouds, contrails, aircraft and
+  ground: direct beam through a Kasten-Young air mass with Rayleigh, ozone and
+  aerosol extinction, diffuse skylight, moonlight, a starlight floor and aerial
+  perspective. Sun and moon come from the real positions (SunCalc) for
+  `CONFIG.location`, or from an accelerated 24 h simulation (`CONFIG.day`).
+- **Theme-tinted lighting**: each theme may pull the physical colours toward
+  its own palette and set its own day/night exposure, without replacing the
+  physics (`window.THEMES[...].lighting`).
+- **Shadows**: moving cloud shadows sampled from the same cloud field the sky
+  renders, plus terrain self-shadowing over the DEM height field.
+- **Realistic night sky**: ~8700 stars from the Yale Bright Star Catalogue
+  (points sized by magnitude, coloured by temperature), rotated at the sidereal
+  rate for the site's latitude, a Milky Way band and a phase-correct moon.
+- **Aircraft**: low-poly jets (CC0 model) on curved routes between real
+  airfields, with a destination rolled at every take-off, sun-lit silhouettes
+  and contrails by day, strobing position lights by night.
+- **Night lights**: vehicle lights moving along the real road network (Overpass)
+  with correct driving side per country, and settlement lights from OSM place
+  nodes (bigger towns get more and brighter dots). Both fade in light by light
+  across twilight instead of switching as one block.
+- **Live weather** (Open-Meteo): current conditions plus a 4-day forecast
+  widget; the weather code selects the cloud coverage and the colour mood.
+- **Fully cached, offline-capable**: basemap tiles, the elevation grid, Overpass
+  road/place cells, the merged road chains and the decoded settlement list live
+  permanently in IndexedDB; the star catalogue is inlined. Once warm, the scene
+  renders fully offline (only weather is fetched live), and a 15-minute cycle
+  transparently retries anything that previously failed.
+- **Pixel-art rendering option**: `CONFIG.renderScale` renders the 3D scene at
+  a fraction of the display size and upscales it in exact integer blocks with
+  `image-rendering: pixelated`, while the DOM UI stays crisp.
+- **Location-aware**: set `CONFIG.location.lat/lon` and everything (flight
+  anchor, terrain tiles, sun/moon, weather, star rotation, traffic side) is
+  derived from it. Without a location, browser geolocation is tried, falling
+  back to the built-in default.
+- Six UI languages, CSS-swappable colour themes, configurable clock format,
+  optional debug panel.
 
 ## Run with Docker (recommended)
 
@@ -47,112 +55,122 @@ docker compose up --build
 
 Then open <http://localhost:58881/>.
 
-The bundled nginx config (`default.conf`) is more than a file server: it
-provides CORS proxies for the tile sources (`/esri/`, `/carto/`,
-`/terrarium/`) that the scene needs for basemap and elevation data.
-A plain static server without these proxies (e.g.
-`python3 -m http.server 58881`) will run the UI but terrain and map
-tiles will fail to load.
+The bundled nginx config (`default.conf`) is more than a file server:
+
+- CORS proxies for the basemap styles (`/esri/streets/`, `/esri/imagery/`) and
+  the elevation tiles (`/terrarium/`).
+- CORS proxies for the three Overpass mirrors (`/overpass/api/`,
+  `/overpass/coffee/`, `/overpass/mail/`) with a browser-like request, long
+  timeouts and a 30-day `proxy_cache` (`overpass-cache.conf`) that also serves
+  stale entries while a mirror is down. Public Overpass instances refuse or
+  mis-handle cross-origin POSTs, and they are flaky; the cache means a cell the
+  browser already paid for is never lost.
+- `Cache-Control: no-store` for HTML and JS, so a changed `CONFIG` takes effect
+  on reload.
+
+A plain static server without these proxies (e.g. `python3 -m http.server
+58881`) runs the UI, but terrain, basemap and road data will not load.
 
 ## Single-file build
 
-`build.py` bundles everything into one self-contained HTML file
-(`background-standalone.html`) — all scripts, the star catalogue and all
-theme CSS are inlined, and theme switching keeps working:
+`build.py` bundles everything into one self-contained HTML file: all scripts,
+the star catalogue and every theme stylesheet are inlined, and theme switching
+keeps working.
 
 ```sh
-python3 build.py            # -> background-standalone.html (no sibling files needed)
+python3 build.py                    # -> background-standalone.html
+python3 build.py out.html           # -> custom output path
+python3 build.py --check            # build to a temp file and verify, write nothing
 ```
 
-Runtime *data* is still fetched at load (tiles, Overpass, weather): serve
-the file from the Docker image for the full experience; opened via
-`file://` or a proxy-less server it renders sky, clouds and UI with an
-"OFFLINE"-labelled ground grid instead of basemap tiles.
+`--check` fails if anything is left that would need a sibling file (an external
+`<script src>` or a CSS `<link>`).
+
+Runtime *data* is still fetched at load (tiles, Overpass, weather): serve the
+file from the Docker image for the full experience. Opened via `file://` or a
+proxy-less server it renders sky, clouds and UI with an "OFFLINE"-labelled
+ground grid instead of basemap tiles.
 
 ## Configuration
 
-Edit `config.js` and reload. All keys (with defaults):
+`config.js` is the reference: every key is documented in place, and unused
+options are listed commented-out with example values. Most knobs are read every
+frame, so editing the file and reloading is enough - no rebuild needed.
+
+Groups:
+
+| Group | What it controls |
+| --- | --- |
+| `theme`, `language`, `timeFormat`, `units`, `credits` | palette, UI language, clock format, °C/°F, attribution line |
+| `debug` | debug panel (weather, shader counters, theme palette and lighting) |
+| `renderScale`, `maxFps` | internal 3D resolution and frame cap |
+| `location` | `lat`/`lon` (+ optional `label`) - everything geographic |
+| `weatherSim`, `weatherSimInterval` | ignore the API and cycle the weather looks |
+| `tiles` | basemap re-fetch interval (`expireDays`), tile-border debug overlay |
+| `ground.style` | `'satellite'` (ESRI World_Imagery) or `'streets'` (ESRI World_Street_Map) |
+| `orbit` | figure-eight path, `radiusKm`, direction, reorientation, `altBob` |
+| `fog.distanceKm` | distance haze (0/false = off) |
+| `clouds` | deck height (`top`/`bottom` in world units) and `density` per weather level |
+| `flights` | aircraft count, altitudes, speeds, destination weights, contrails, night strobes |
+| `terrain` | DEM mesh, `exaggeration`, `edgeFadeTiles`, `carLights`, `cityLights`, `wireframe` |
+| `carLights` | road width, light sizes, lane separation, traffic range/fade, `trafficSide`, spacing, speed, density, brightness |
+| `lights` | twilight switching window of every artificial light (`offDeg`, `onDeg`, `softDeg`) |
+| `atmosphere` | turbidity, moon/star gains, night floor, albedo/sky/air gains, haze residual, cloud albedo and cloud haze, cloud shadows, terrain shadows |
+| `stars` | star colour `tint` and `brightness` |
+| `day` | `simulation`, `cycleSeconds`, `fixedTime` |
+
+### World scale
+
+1 world unit = one zoom-11 tile ≈ 12.9 km at 48.6°N. World axes are
+`+X = west`, `+Y = up`, `+Z = north`; the camera flies the 15-35 km band
+(`y ≈ 1.16-2.70`). Cloud deck heights, fog distance and orbit radius are all
+expressed in these units or in km where noted.
+
+### Themes and theme lighting
+
+A theme is a stylesheet plus an optional lighting block:
 
 ```javascript
-window.CONFIG = {
-    theme: 'ash',                      // 'ash' | 'gruvbox' | 'nord'
-    language: 'en',                    // 'en' | 'de' | 'it' | 'es' | 'fr' | 'ru'
-    timeFormat: 'DD. MMMM, YYYY \u2012 HH:mm:SS',
-    debug: 0,                          // 1 = show right-side debug panel
-    units: { temperature: 'C' },       // 'C' | 'F'
-    credits: true,                     // data-attribution block in info box
-    renderScale: 1,                    // 0.3..1 internal 3D resolution
-    maxFps: 30,                        // WebGL scene frame cap (0 = free)
-
-    location: {                        // drives scene anchor, sun/moon, weather
-        lat: 51.5074,                  //   -90..+90, north positive
-        lon: -0.1278,                  //   -180..+180, east positive
-        label: ''                      // optional name, skips reverse geocoding
-    },
-
-    day: {
-        simulation: false,             // true: run 24 h in cycleSeconds;
-        cycleSeconds: 20,              // false: real sun/moon positions
-        fixedTime: null                // 'HH:MM' freezes the sim clock at
-                                       // that time of day (cars, clouds,
-                                       // weather keep moving); null = flow
-    },
-    weatherSim: false,                 // true: cycle weather themes, ignore API
-    weatherSimInterval: 30000,         // ms per sim step
-
-    clouds: { top: 0.9, bottom: -0.3 },// cloud deck, world units
-                                       // (1 unit = ~12.9 km at z11 / 48.6 deg N)
-
-    orbit: {                           // null/omit = straight flight
-        radiusKm: 60,                  // lemniscate lobe tip (clamped ~190 km)
-        clockwise: true,
-        reorient: true,                // random heading at each crossing
-        altBob: {                      // vertical bob, flight band 15-35 km
-            enabled: true,             // false = constant 25 km
-            amp: 0.77,                 // half-band in world units
-            periodS: 90,               // seconds per bob cycle
-            tilt: 0.3                  // pitch reaction to climb/descent
-        }
-    },
-    fog: { distanceKm: 120 },          // ground haze; 0/false = off
-
-    terrain: {
-        enabled: true,                 // false = flat plane
-        exaggeration: 8,               // vertical DEM scale factor
-        wireframe: false,              // debug: orange mesh edges
-        nightLights: false,            // NASA VIIRS city-lights overlay
-        carLights: true,               // moving lights on real roads
-        cityLights: true               // settlement glow dots
-    },
-
-    flights: {                         // see section above; all distances km
-        enabled: true,
-        altitudeKm: 14, climbKm: 100,  // cruise / climb-descent run
-        count: 84, speedKmh: 850, speedVar: 0.18, minLegKm: 60,
-        holdMinS: 50, holdMaxS: 150,   // ground hold at destination
-        wHub: 4, wField: 2, wStrip: 1, // destination roll weights
-        contrailChance: 0.6,           // share of aircraft with a trail
-        contrailStartKm: 6,            // formation altitude
-        contrailLifeS: 300,            // visibility duration
-        contrailWidthM: 310            // full trail width
-    },
-
-    ground: { style: 'satellite' },    // 'satellite' | 'streets'
-    tiles: {
-        expireDays: null,              // >0: re-fetch basemap tiles after n days
-        debug: false                   // tile borders + coords on the ground
+window.THEMES['mytheme'] = {
+    css: 'mytheme.css',
+    lighting: {
+        tint: 0.45,          // 0 = pure physics, 1 = theme colour
+        sun: '#f2e3c0',      // direct beam
+        sky: '#5e81ac',      // skylight and horizon
+        air: '#81a1c1',      // aerial perspective / haze
+        moon: '#d8e3ee',     // moonlight
+        gain: 0.95,          // day exposure
+        nightGain: 1.12      // night exposure
     }
 };
 ```
 
+The physical model stays the base in every theme; `lighting` only shifts hues
+and exposure. Omit `lighting` for a purely physical theme. The palette itself is
+read from the CSS custom properties of the active stylesheet, so the scene and
+the UI always agree.
+
+### Debug switches
+
+All off by default, all documented in `config.js`:
+
+- `debug: 1` - debug panel (bottom left): weather state, sun/moon, shader
+  counters, the active theme palette and its lighting values.
+- `tiles: { debug: true }` - bake tile borders, N/S and x/y labels into the
+  ground texture (orientation check).
+- `terrain: { wireframe: true }` - draw the mesh edges.
+- `ground: { style: 'streets' }` - labelled street map instead of satellite.
+- `day: { simulation: true }` / `weatherSim: true` - deterministic day cycle and
+  weather cycle for comparing looks.
+
 ## URL hash parameters
 
 `http://host:58881/#flight=N&fetch=S`
 
-- `flight=N|NE|E|SE|S|SW|W|NW` — heading of the straight flight corridor
-  (used when `CONFIG.orbit` is disabled)
-- `fetch=N|NE|E|SE|S|SW|W|NW` — direction the tile mosaic is prefetched
-  ahead of the camera
+- `flight=N|NE|E|SE|S|SW|W|NW` - heading of the straight flight corridor (used
+  when `CONFIG.orbit` is disabled)
+- `fetch=N|NE|E|SE|S|SW|W|NW` - direction the tile mosaic is prefetched ahead of
+  the camera
 
 ## Time format tokens
 
@@ -173,42 +191,54 @@ needs no special token).
 \n     newline    \t tab    \\ literal backslash
 ```
 
-## Adding a new language
+## Caches
 
-Edit `i18n.js` and add entries for each existing key under your new
-language code, e.g.:
+Everything is stored in IndexedDB, database `background-tiles`, store `tiles`:
+
+| Key pattern | Content |
+| --- | --- |
+| `sat/{z}/{x}/{y}` / `{z}/{x}/{y}` | basemap tiles, kept per style so satellite and street maps cache separately |
+| `elev/...` | decoded elevation grid cells |
+| `geo/mw11/...`, `geo/mw_e/...`, `geo/sec10/...` | Overpass road cells (motorway network and side roads) |
+| `geo/place_...` | Overpass place-node cells |
+| `geo/roadchains_v1` | merged road polylines (rebuilt only when a cell is re-fetched) |
+| `geo/placecache_v1` | decoded settlement list |
+| `geo/airports_v1` | airfield list used by the aviation layer |
+
+The star catalogue is not cached: `build.py` inlines `vendor/stars.json` into
+`window.__starsData`. Weather is the only thing fetched live on every load.
+
+Cached data is never re-fetched unless `CONFIG.tiles.expireDays` is set. To
+start clean, delete the `background-tiles` database in the browser.
+
+## Adding a language
+
+Add the key under the new language code in `i18n.js`:
 
 ```javascript
 window.TRANSLATIONS['Sunrise']['xx'] = 'MyTranslation';
 ```
 
-## Adding a new theme
-
-Drop a new `*.css` file next to the others and add an entry to
-`window.THEMES` in `config.js`:
-
-```javascript
-window.THEMES['mytheme'] = 'mytheme.css';
-```
-
 ## Files
 
 ```
 .
-├── background.html          the page (UI, weather, day/night driver)
-├── config.js                user-facing configuration
+├── background.html          the page (UI, weather, day/night driver, debug panel)
+├── config.js                user-facing configuration + window.THEMES
 ├── i18n.js                  translation strings (en/de/it/es/fr/ru)
-├── ash.css                  default color theme
-├── gruvbox.css              alternative color theme
-├── nord.css                 alternative color theme
+├── ash.css                  default colour theme
+├── gruvbox.css              alternative colour theme
+├── nord.css                 alternative colour theme
 ├── vendor/
-│   ├── clouds3d.js          WebGL scene renderer (clouds, terrain, sky, lights)
-│   ├── suncalc.js           ISC (SunCalc by mourner)
+│   ├── clouds3d.js          WebGL scene renderer (sky, clouds, terrain, lights)
+│   ├── suncalc.js           sun/moon positions - ISC (SunCalc by mourner)
+│   ├── plane3d.js           low-poly aircraft model - CC0
 │   ├── stars.json           Yale Bright Star Catalogue subset
 │   └── LICENSE              per-library license attributions
-├── default.conf             nginx config: port 58881 + tile CORS proxies
+├── default.conf             nginx: port 58881, CORS proxies, cache headers
+├── overpass-cache.conf      nginx proxy_cache_path for the Overpass cache
 ├── build.py                 single-file HTML bundler (see "Single-file build")
-├── Dockerfile               builds nginx:alpine image
+├── Dockerfile               builds the nginx:alpine image
 ├── docker-compose.yml       one-service Compose file
 └── LICENSE                  MIT (application code)
 ```
@@ -217,11 +247,15 @@ window.THEMES['mytheme'] = 'mytheme.css';
 
 - **Background application code**: MIT (see `LICENSE`)
 - **SunCalc** (vendored): ISC - <https://github.com/mourner/suncalc>
+- **Aircraft model** (`vendor/plane3d.js`): CC0
 - **Open-Meteo** (weather API): CC BY 4.0 - <https://open-meteo.com/>
-- **OpenStreetMap** (basemap tiles via ESRI/Carto, Overpass road and
-  place data): ODbL - <https://www.openstreetmap.org/copyright>
-- **Copernicus DEM** (terrain via Mapzen terrarium tiles): open data
-- **NASA GIBS VIIRS** (optional night-lights overlay): public domain
+- **ESRI** basemaps (`World_Imagery`, `World_Street_Map`) served through the
+  bundled proxy: Esri, its licensors and contributors -
+  <https://www.esri.com/en-us/legal/acknowledgmentsandstandards>
+- **OpenStreetMap** (Overpass road and place data): ODbL -
+  <https://www.openstreetmap.org/copyright>
+- **Copernicus DEM** (terrain, via Mapzen/TILEZEN terrarium tiles): open data -
+  <https://registry.opendata.aws/terrain-tiles/>
 - **Yale Bright Star Catalogue** (star positions, via `vendor/stars.json`)
 - **OpenStreetMap Nominatim** (reverse geocoding): ODbL -
   <https://nominatim.org/release/>
diff --git a/default.conf b/default.conf
index e8e5027..a8d3579 100644
--- a/default.conf
+++ b/default.conf
@@ -23,25 +23,12 @@ server {
         access_log off;
     }
 
-    # CORS proxy for Carto basemaps (place names, OSM-derived).
-    # URL format: /carto/voyager/{z}/{x}/{y}.png
-    location ^~ /carto/ {
-        resolver 1.1.1.1 8.8.8.8 ipv6=off valid=300s;
-        proxy_pass https://a.basemaps.cartocdn.com/;
-        proxy_ssl_server_name on;
-        proxy_set_header Host a.basemaps.cartocdn.com;
-        proxy_set_header User-Agent "Mozilla/5.0 (compatible; tile-proxy)";
-        add_header Access-Control-Allow-Origin "*" always;
-        add_header Access-Control-Allow-Methods "GET, HEAD, OPTIONS" always;
-        add_header Access-Control-Max-Age 86400 always;
-    }
-
-    # CORS proxy for ESRI World_Street_Map. URL format:
-    # /esri/wsm/{z}/{y}/{x}.jpg -> ESRI /ArcGIS/.../World_Street_Map/.../tile/{z}/{y}/{x}
+    # CORS proxies for the two basemap styles the scene can use.
+    # /esri/streets/{z}/{y}/{x}.jpg  -> ESRI World_Street_Map (place names)
+    # /esri/imagery/{z}/{y}/{x}.jpg  -> ESRI World_Imagery (aerial)
     location ^~ /esri/ {
         resolver 1.1.1.1 8.8.8.8 ipv6=off valid=300s;
         rewrite ^/esri/streets/(.*)$ /ArcGIS/rest/services/World_Street_Map/MapServer/tile/$1 break;
-        rewrite ^/esri/topo/(.*)$ /ArcGIS/rest/services/World_Topo_Map/MapServer/tile/$1 break;
         rewrite ^/esri/imagery/(.*)$ /ArcGIS/rest/services/World_Imagery/MapServer/tile/$1 break;
         proxy_pass https://server.arcgisonline.com;
         proxy_ssl_server_name on;
diff --git a/docker-compose.yml b/docker-compose.yml
index e38eebf..d1a6bfa 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -1,4 +1,3 @@
-version: '3.8'
 
 services:
   wireframe: