diff --git a/frontend/src/components/layout/AppSidebar.vue b/frontend/src/components/layout/AppSidebar.vue
index 89dd4ef8de..dad127b06b 100644
--- a/frontend/src/components/layout/AppSidebar.vue
+++ b/frontend/src/components/layout/AppSidebar.vue
@@ -7,20 +7,18 @@
     ]"
   >
     <!-- Logo/Brand -->
-    <div class="sidebar-header">
+    <div class="sidebar-header" :class="{ 'sidebar-header-collapsed': sidebarCollapsed }">
       <!-- Custom Logo or Default Logo -->
-      <div class="flex h-9 w-9 items-center justify-center overflow-hidden rounded-xl shadow-glow">
+      <div class="sidebar-logo flex h-9 w-9 items-center justify-center overflow-hidden rounded-xl shadow-glow">
         <img v-if="settingsLoaded" :src="siteLogo || '/logo.png'" alt="Logo" class="h-full w-full object-contain" />
       </div>
-      <transition name="fade">
-        <div v-if="!sidebarCollapsed" class="flex flex-col">
-          <span class="text-lg font-bold text-gray-900 dark:text-white">
-            {{ siteName }}
-          </span>
-          <!-- Version Badge -->
-          <VersionBadge :version="siteVersion" />
-        </div>
-      </transition>
+      <div class="sidebar-brand" :class="{ 'sidebar-brand-collapsed': sidebarCollapsed }" :aria-hidden="sidebarCollapsed ? 'true' : 'false'">
+        <span class="sidebar-brand-title text-lg font-bold text-gray-900 dark:text-white">
+          {{ siteName }}
+        </span>
+        <!-- Version Badge -->
+        <VersionBadge :version="siteVersion" />
+      </div>
     </div>
 
     <!-- Navigation -->
@@ -35,17 +33,25 @@
               <button
                 type="button"
                 class="sidebar-link mb-1 w-full"
-                :class="{ 'sidebar-link-active': isGroupActive(item) && !isGroupExpanded(item) }"
+                :class="{
+                  'sidebar-link-active': isGroupActive(item) && !isGroupExpanded(item),
+                  'sidebar-link-collapsed': sidebarCollapsed
+                }"
                 :title="sidebarCollapsed ? item.label : undefined"
                 @click="sidebarCollapsed ? undefined : toggleGroup(item)"
               >
                 <component :is="item.icon" class="h-5 w-5 flex-shrink-0" />
-                <transition name="fade">
-                  <span v-if="!sidebarCollapsed" class="flex flex-1 items-center justify-between">
-                    <span>{{ item.label }}</span>
-                    <ChevronDownIcon class="h-4 w-4 flex-shrink-0 transition-transform duration-200" :class="isGroupExpanded(item) ? 'rotate-180' : ''" />
-                  </span>
-                </transition>
+                <span
+                  class="sidebar-label sidebar-label-flex"
+                  :class="{ 'sidebar-label-collapsed': sidebarCollapsed }"
+                  :aria-hidden="sidebarCollapsed ? 'true' : 'false'"
+                >
+                  <span class="min-w-0 truncate">{{ item.label }}</span>
+                  <ChevronDownIcon
+                    class="h-4 w-4 flex-shrink-0 transition-transform duration-200"
+                    :class="isGroupExpanded(item) ? 'rotate-180' : ''"
+                  />
+                </span>
               </button>
               <!-- Children -->
               <div v-if="!sidebarCollapsed && isGroupExpanded(item)" class="mb-1 ml-4 border-l border-gray-200 pl-2 dark:border-dark-600">
@@ -67,7 +73,7 @@
               v-else
               :to="item.path"
               class="sidebar-link mb-1"
-              :class="{ 'sidebar-link-active': isActive(item.path) }"
+              :class="{ 'sidebar-link-active': isActive(item.path), 'sidebar-link-collapsed': sidebarCollapsed }"
               :title="sidebarCollapsed ? item.label : undefined"
               :id="
                 item.path === '/admin/accounts'
@@ -82,35 +88,32 @@
             >
               <span v-if="item.iconSvg" class="h-5 w-5 flex-shrink-0 sidebar-svg-icon" v-html="sanitizeSvg(item.iconSvg)"></span>
               <component v-else :is="item.icon" class="h-5 w-5 flex-shrink-0" />
-              <transition name="fade">
-                <span v-if="!sidebarCollapsed">{{ item.label }}</span>
-              </transition>
+              <span class="sidebar-label" :class="{ 'sidebar-label-collapsed': sidebarCollapsed }" :aria-hidden="sidebarCollapsed ? 'true' : 'false'">{{ item.label }}</span>
             </router-link>
           </template>
         </div>
 
         <!-- Personal Section for Admin (hidden in simple mode) -->
         <div v-if="!authStore.isSimpleMode" class="sidebar-section">
-          <div v-if="!sidebarCollapsed" class="sidebar-section-title">
-            {{ t('nav.myAccount') }}
+          <div class="sidebar-section-title" :class="{ 'sidebar-section-title-collapsed': sidebarCollapsed }" :aria-hidden="sidebarCollapsed ? 'true' : 'false'">
+            <span class="sidebar-section-title-text" :class="{ 'sidebar-section-title-text-collapsed': sidebarCollapsed }">
+              {{ t('nav.myAccount') }}
+            </span>
           </div>
-          <div v-else class="mx-3 my-3 h-px bg-gray-200 dark:bg-dark-700"></div>
 
           <router-link
             v-for="item in personalNavItems"
             :key="item.path"
             :to="item.path"
             class="sidebar-link mb-1"
-            :class="{ 'sidebar-link-active': isActive(item.path) }"
+            :class="{ 'sidebar-link-active': isActive(item.path), 'sidebar-link-collapsed': sidebarCollapsed }"
             :title="sidebarCollapsed ? item.label : undefined"
             :data-tour="item.path === '/keys' ? 'sidebar-my-keys' : undefined"
             @click="handleMenuItemClick(item.path)"
           >
             <span v-if="item.iconSvg" class="h-5 w-5 flex-shrink-0 sidebar-svg-icon" v-html="sanitizeSvg(item.iconSvg)"></span>
             <component v-else :is="item.icon" class="h-5 w-5 flex-shrink-0" />
-            <transition name="fade">
-              <span v-if="!sidebarCollapsed">{{ item.label }}</span>
-            </transition>
+            <span class="sidebar-label" :class="{ 'sidebar-label-collapsed': sidebarCollapsed }" :aria-hidden="sidebarCollapsed ? 'true' : 'false'">{{ item.label }}</span>
           </router-link>
         </div>
       </template>
@@ -123,16 +126,14 @@
             :key="item.path"
             :to="item.path"
             class="sidebar-link mb-1"
-            :class="{ 'sidebar-link-active': isActive(item.path) }"
+            :class="{ 'sidebar-link-active': isActive(item.path), 'sidebar-link-collapsed': sidebarCollapsed }"
             :title="sidebarCollapsed ? item.label : undefined"
             :data-tour="item.path === '/keys' ? 'sidebar-my-keys' : undefined"
             @click="handleMenuItemClick(item.path)"
           >
             <span v-if="item.iconSvg" class="h-5 w-5 flex-shrink-0 sidebar-svg-icon" v-html="sanitizeSvg(item.iconSvg)"></span>
             <component v-else :is="item.icon" class="h-5 w-5 flex-shrink-0" />
-            <transition name="fade">
-              <span v-if="!sidebarCollapsed">{{ item.label }}</span>
-            </transition>
+            <span class="sidebar-label" :class="{ 'sidebar-label-collapsed': sidebarCollapsed }" :aria-hidden="sidebarCollapsed ? 'true' : 'false'">{{ item.label }}</span>
           </router-link>
         </div>
       </template>
@@ -144,28 +145,26 @@
       <button
         @click="toggleTheme"
         class="sidebar-link mb-2 w-full"
+        :class="{ 'sidebar-link-collapsed': sidebarCollapsed }"
         :title="sidebarCollapsed ? (isDark ? t('nav.lightMode') : t('nav.darkMode')) : undefined"
       >
         <SunIcon v-if="isDark" class="h-5 w-5 flex-shrink-0 text-amber-500" />
         <MoonIcon v-else class="h-5 w-5 flex-shrink-0" />
-        <transition name="fade">
-          <span v-if="!sidebarCollapsed">{{
-            isDark ? t('nav.lightMode') : t('nav.darkMode')
-          }}</span>
-        </transition>
+        <span class="sidebar-label" :class="{ 'sidebar-label-collapsed': sidebarCollapsed }" :aria-hidden="sidebarCollapsed ? 'true' : 'false'">{{
+          isDark ? t('nav.lightMode') : t('nav.darkMode')
+        }}</span>
       </button>
 
       <!-- Collapse Button -->
       <button
         @click="toggleSidebar"
         class="sidebar-link w-full"
+        :class="{ 'sidebar-link-collapsed': sidebarCollapsed }"
         :title="sidebarCollapsed ? t('nav.expand') : t('nav.collapse')"
       >
         <ChevronDoubleLeftIcon v-if="!sidebarCollapsed" class="h-5 w-5 flex-shrink-0" />
         <ChevronDoubleRightIcon v-else class="h-5 w-5 flex-shrink-0" />
-        <transition name="fade">
-          <span v-if="!sidebarCollapsed">{{ t('nav.collapse') }}</span>
-        </transition>
+        <span class="sidebar-label" :class="{ 'sidebar-label-collapsed': sidebarCollapsed }" :aria-hidden="sidebarCollapsed ? 'true' : 'false'">{{ t('nav.collapse') }}</span>
       </button>
     </div>
   </aside>
@@ -794,14 +793,120 @@ onMounted(() => {
 </script>
 
 <style scoped>
-.fade-enter-active,
-.fade-leave-active {
-  transition: opacity 0.2s ease;
+.sidebar-logo {
+  flex: 0 0 2.25rem;
+  min-width: 2.25rem;
 }
 
-.fade-enter-from,
-.fade-leave-to {
+.sidebar-header-collapsed {
+  gap: 0;
+  padding-left: 1.125rem;
+  padding-right: 1.125rem;
+}
+
+.sidebar-brand {
+  min-width: 0;
+  flex: 1 1 auto;
+  overflow: hidden;
+  white-space: nowrap;
+  transition:
+    max-width 0.22s ease,
+    opacity 0.14s ease,
+    transform 0.14s ease;
+  max-width: 12rem;
+}
+
+.sidebar-brand-collapsed {
+  max-width: 0;
   opacity: 0;
+  transform: translateX(-4px);
+  pointer-events: none;
+}
+
+.sidebar-brand-title {
+  display: block;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.sidebar-link-collapsed {
+  gap: 0;
+  padding-left: 0.875rem;
+  padding-right: 0.875rem;
+}
+
+.sidebar-section-title {
+  position: relative;
+  display: flex;
+  align-items: center;
+  min-height: 1.25rem;
+  overflow: hidden;
+  white-space: nowrap;
+}
+
+.sidebar-section-title-text {
+  display: block;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  transition:
+    opacity 0.16s ease,
+    transform 0.16s ease;
+}
+
+.sidebar-section-title::after {
+  content: '';
+  position: absolute;
+  left: 0.75rem;
+  right: 0.75rem;
+  top: 50%;
+  height: 1px;
+  background: rgb(229 231 235);
+  opacity: 0;
+  transform: translateY(-50%);
+  transition: opacity 0.18s ease;
+}
+
+.dark .sidebar-section-title::after {
+  background: rgb(55 65 81);
+}
+
+.sidebar-section-title-text-collapsed {
+  opacity: 0;
+  transform: translateX(-4px);
+}
+
+.sidebar-section-title-collapsed::after {
+  opacity: 1;
+  transition-delay: 0.08s;
+}
+
+.sidebar-label {
+  display: block;
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  transition:
+    max-width 0.2s ease,
+    opacity 0.12s ease,
+    transform 0.12s ease;
+  max-width: 12rem;
+}
+
+.sidebar-label-flex {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 0.5rem;
+}
+
+.sidebar-label-collapsed {
+  max-width: 0;
+  opacity: 0;
+  transform: translateX(-4px);
+  pointer-events: none;
 }
 
 /* Custom SVG icon in sidebar: constrain size without overriding uploaded SVG colors */
diff --git a/frontend/src/style.css b/frontend/src/style.css
index f956400ff3..59c6d1822e 100644
--- a/frontend/src/style.css
+++ b/frontend/src/style.css
@@ -523,12 +523,17 @@
     @apply border-r border-gray-200 dark:border-dark-800;
     @apply flex flex-col;
     @apply transition-transform duration-300;
+    transition-property: width, transform;
   }
 
   .sidebar-header {
     @apply h-16 px-6;
     @apply flex items-center gap-3;
+    @apply overflow-hidden;
     @apply border-b border-gray-100 dark:border-dark-800;
+    transition:
+      padding 0.2s ease,
+      gap 0.2s ease;
   }
 
   .sidebar-nav {
@@ -536,12 +541,15 @@
   }
 
   .sidebar-link {
-    @apply flex items-center gap-3 rounded-xl px-3 py-2.5;
+    @apply flex items-center gap-3 rounded-xl py-2.5;
+    @apply overflow-hidden;
     @apply text-sm font-medium;
     @apply text-gray-600 dark:text-dark-300;
     @apply transition-all duration-200;
     @apply hover:bg-gray-100 dark:hover:bg-dark-800;
     @apply hover:text-gray-900 dark:hover:text-white;
+    padding-left: 1.0625rem;
+    padding-right: 0.875rem;
   }
 
   .sidebar-link-active {