diff --git a/scripts/build.mjs b/scripts/build.mjs
index 7282e364..611738cb 100644
--- a/scripts/build.mjs
+++ b/scripts/build.mjs
@@ -89,7 +89,7 @@ async function build() {
     }
     await buildCssBundles(legacy ? buildCssLegacy : buildCss, themes);
     if (offline) {
-        await buildOffline(version, bundleName);
+        await buildOffline(version, bundleName, themeAssets);
     }
 
     console.log(`built ${PROJECT_ID}${legacy ? " legacy" : ""} ${version} successfully`);
@@ -196,9 +196,17 @@ async function buildJsLegacy(bundleName) {
     });
 }
 
-async function buildOffline(version, bundleName) {
+async function buildOffline(version, bundleName, themeAssets) {
+    const {offlineAssets, cacheAssets} = themeAssets.reduce((result, asset) => {
+        if (asset.endsWith(".css")) {
+            result.offlineAssets.push(asset);
+        } else {
+            result.cacheAssets.push(asset);
+        }
+        return result;
+    }, {offlineAssets: [], cacheAssets: []});
     // write offline availability
-    const offlineFiles = [bundleName, `${PROJECT_ID}.css`, "index.html", "icon-192.png"];
+    const offlineFiles = [bundleName, `${PROJECT_ID}.css`, "index.html", "icon-192.png"].concat(offlineAssets);
 
     // write appcache manifest
     const manifestLines = [
@@ -214,7 +222,8 @@ async function buildOffline(version, bundleName) {
     // write service worker
     let swSource = await fs.readFile(path.join(projectDir, "src/service-worker.template.js"), "utf8");
     swSource = swSource.replace(`"%%VERSION%%"`, `"${version}"`);
-    swSource = swSource.replace(`"%%FILES%%"`, JSON.stringify(offlineFiles));
+    swSource = swSource.replace(`"%%OFFLINE_FILES%%"`, JSON.stringify(offlineFiles));
+    swSource = swSource.replace(`"%%CACHE_FILES%%"`, JSON.stringify(cacheAssets));
     await fs.writeFile(path.join(targetDir, "sw.js"), swSource, "utf8");
     // write web manifest
     const webManifest = {
diff --git a/src/service-worker.template.js b/src/service-worker.template.js
index 331f5cb7..0ccca862 100644
--- a/src/service-worker.template.js
+++ b/src/service-worker.template.js
@@ -15,13 +15,17 @@ limitations under the License.
 */
 
 const VERSION = "%%VERSION%%";
-const FILES = "%%FILES%%";
 const cacheName = `brawl-${VERSION}`;
+const OFFLINE_FILES = "%%OFFLINE_FILES%%";
+// TODO: cache these files when requested
+// The difficulty is that these are relative filenames, and we don't have access to document.baseURI
+// Clients.match({type: "window"}).url and assume they are all the same? they really should be ... safari doesn't support this though
+const CACHE_FILES = "%%CACHE_FILES%%";
 
 self.addEventListener('install', function(e) {
     e.waitUntil(
         caches.open(cacheName).then(function(cache) {
-            return cache.addAll(FILES);
+            return cache.addAll(OFFLINE_FILES);
         })
     );
 });