diff --git a/.vitepress/theme/InstallApp.vue b/.vitepress/theme/InstallApp.vue
index 07d48bf..d208f51 100644
--- a/.vitepress/theme/InstallApp.vue
+++ b/.vitepress/theme/InstallApp.vue
@@ -1,26 +1,39 @@
 <script setup lang="ts">
-import { computed, onMounted, ref } from 'vue'
-import { useRoute } from 'vitepress'
+import { computed, onMounted, onUnmounted, ref } from 'vue'
 
-const route = useRoute()
-const showAndroidInstall = ref(false)
-const showIOSHint = ref(false)
+type InstallMode = 'native' | 'ios' | 'android-menu' | 'desktop' | 'https-required'
+
+const showInstall = ref(false)
 const dismissed = ref(false)
+const installMode = ref<InstallMode | null>(null)
 const isMobile = ref(false)
 let deferredPrompt: BeforeInstallPromptEvent | null = null
+let fallbackTimer: ReturnType<typeof setTimeout> | null = null
 
 interface BeforeInstallPromptEvent extends Event {
   prompt: () => Promise<void>
   userChoice: Promise<{ outcome: 'accepted' | 'dismissed' }>
 }
 
-const isDocPage = computed(() => route.path !== '/')
+const visible = computed(() => !dismissed.value && showInstall.value && installMode.value !== null)
 
-const visible = computed(() => {
-  if (dismissed.value) return false
-  if (isMobile.value && isDocPage.value) return false
-  return showAndroidInstall.value || showIOSHint.value
-})
+function needsHttpsForInstall() {
+  return (
+    !window.isSecureContext &&
+    !['localhost', '127.0.0.1'].includes(location.hostname)
+  )
+}
+
+function onBeforeInstallPrompt(event: Event) {
+  event.preventDefault()
+  deferredPrompt = event as BeforeInstallPromptEvent
+  installMode.value = 'native'
+  showInstall.value = true
+  if (fallbackTimer) {
+    clearTimeout(fallbackTimer)
+    fallbackTimer = null
+  }
+}
 
 onMounted(() => {
   isMobile.value = window.matchMedia('(max-width: 768px)').matches
@@ -38,15 +51,29 @@ onMounted(() => {
 
   const isIOS = /iPad|iPhone|iPod/.test(navigator.userAgent)
   if (isIOS) {
-    showIOSHint.value = true
+    installMode.value = 'ios'
+    showInstall.value = true
     return
   }
 
-  window.addEventListener('beforeinstallprompt', (event) => {
-    event.preventDefault()
-    deferredPrompt = event as BeforeInstallPromptEvent
-    showAndroidInstall.value = true
-  })
+  if (needsHttpsForInstall()) {
+    installMode.value = 'https-required'
+    showInstall.value = true
+    return
+  }
+
+  window.addEventListener('beforeinstallprompt', onBeforeInstallPrompt)
+
+  fallbackTimer = setTimeout(() => {
+    if (deferredPrompt || installMode.value) return
+    installMode.value = isMobile.value ? 'android-menu' : 'desktop'
+    showInstall.value = true
+  }, 2500)
+})
+
+onUnmounted(() => {
+  window.removeEventListener('beforeinstallprompt', onBeforeInstallPrompt)
+  if (fallbackTimer) clearTimeout(fallbackTimer)
 })
 
 async function installApp() {
@@ -54,7 +81,7 @@ async function installApp() {
   await deferredPrompt.prompt()
   await deferredPrompt.userChoice
   deferredPrompt = null
-  showAndroidInstall.value = false
+  showInstall.value = false
 }
 
 function dismiss() {
@@ -66,15 +93,24 @@ function dismiss() {
 <template>
   <div v-if="visible" class="install-app">
     <div class="install-app__content">
-      <p v-if="showAndroidInstall" class="install-app__text">
+      <p v-if="installMode === 'native'" class="install-app__text">
         可将「道德经」安装到桌面，像 App 一样使用。
       </p>
-      <p v-else class="install-app__text">
+      <p v-else-if="installMode === 'ios'" class="install-app__text">
         iPhone：Safari 底部分享 →「添加到主屏幕」，阅读更方便。
       </p>
+      <p v-else-if="installMode === 'android-menu'" class="install-app__text">
+        Android：Chrome 右上角菜单 →「安装应用」或「添加到主屏幕」。
+      </p>
+      <p v-else-if="installMode === 'desktop'" class="install-app__text">
+        电脑：地址栏右侧点击「安装」图标，或浏览器菜单 →「安装道德经」。
+      </p>
+      <p v-else class="install-app__text">
+        安装应用需通过 HTTPS 域名访问（内网 http://IP 地址只能添加快捷方式，无法真正安装）。
+      </p>
       <div class="install-app__actions">
         <button
-          v-if="showAndroidInstall"
+          v-if="installMode === 'native'"
           type="button"
           class="install-app__primary"
           @click="installApp"
diff --git a/server/index.js b/server/index.js
index c47d23c..e49f655 100644
--- a/server/index.js
+++ b/server/index.js
@@ -104,6 +104,7 @@ const PUBLIC_PATHS = new Set([
 function isPublicPath(reqPath) {
   if (PUBLIC_PATHS.has(reqPath)) return true
   if (reqPath.startsWith('/assets/')) return true
+  if (reqPath.startsWith('/images/')) return true
   if (reqPath === '/sw.js' || reqPath.endsWith('.webmanifest')) return true
   if (/^\/workbox-[\w-]+\.js$/.test(reqPath)) return true
   return false