diff --git a/renderer/app.js b/renderer/app.js
index 6e496a9..8191b5f 100644
--- a/renderer/app.js
+++ b/renderer/app.js
@@ -4936,12 +4936,13 @@ function _buildHosterSettingsHtml(name) {
   const hs = (config.hosterSettings && config.hosterSettings[name]) || {};
   const maxSpeedMbs = hs.maxSpeedKbs > 0 ? String(+(hs.maxSpeedKbs / 1024).toFixed(2)) : '0';
   return `<div class="account-hoster-settings">
-    <div class="account-hoster-settings-header" data-hoster-settings-toggle="${name}">
+    <div class="account-hoster-settings-header" data-hoster-settings-toggle="${name}" aria-expanded="false">
       <span class="panel-arrow">&#9654;</span>
       <span>Upload-Einstellungen</span>
     </div>
-    <div class="account-hoster-settings-body" style="display:none">
-      <div class="settings-grid-mini">
+    <div class="account-hoster-settings-body account-collapse" aria-hidden="true" inert>
+      <div class="account-collapse-content">
+        <div class="account-hoster-settings-body-inner settings-grid-mini">
         <div class="settings-row">
           <label>Retries</label>
           <input type="number" class="hs-input" data-hoster="${name}" data-hs="retries" value="${hs.retries ?? 3}" min="0" max="500">
@@ -4984,6 +4985,7 @@ function _buildHosterSettingsHtml(name) {
           <input type="checkbox" class="hs-input" data-hoster="${name}" data-hs="sizeMemoEnabled" ${hs.sizeMemoEnabled !== false ? 'checked' : ''}>
           <span class="hint">Überspringt nach zwei verdächtigen Ablehnungen auf einem Account größere Dateien dort vorab ("Bekanntes Größen-Limit"). Abschalten = jede Datei wird immer wirklich versucht.</span>
         </div>
+        </div>
       </div>
     </div>
   </div>`;
@@ -4994,17 +4996,15 @@ function _buildAccountHosterGroupHtml(name, accounts) {
   const isOpen = _hosterGroupOpenState(name, summary);
   const dot = window.AccountStatus.getAccountGroupStatus(summary);
   const countLabel = `${summary.ok}/${summary.total}`;
-  const arrow = isOpen ? '&#9660;' : '&#9654;';
   let cardsHtml = '';
   accounts.forEach((account, idx) => { cardsHtml += _buildAccountCardHtml(name, account, idx); });
-  const bodyStyle = isOpen ? '' : 'style="display:none"';
   const lifeStat = _hosterLifetimeStat(name);
   const lifeMeta = lifeStat && lifeStat.total > 0
     ? `<span class="account-hoster-group-meta" title="Erfolgsrate aus den letzten ${lifeStat.total} Uploads dieses Hosters">${Math.round(lifeStat.rate * 100)}% ok (${lifeStat.total})</span>`
     : '';
   return `<div class="account-hoster-group" data-hoster-group="${name}">
-    <div class="account-hoster-group-header" data-hoster-toggle="${name}">
-      <span class="panel-arrow">${arrow}</span>
+    <div class="account-hoster-group-header" data-hoster-toggle="${name}" aria-expanded="${isOpen}">
+      <span class="panel-arrow">&#9654;</span>
       <span class="account-status-dot status-${dot}"></span>
       <span class="account-hoster-group-title">${escapeHtml(getHosterLabel(name))}</span>
       <span class="account-hoster-group-count">${countLabel}</span>
@@ -5012,7 +5012,9 @@ function _buildAccountHosterGroupHtml(name, accounts) {
       ${summary.error ? `<span class="account-hoster-group-meta error">${summary.error} Fehler</span>` : ''}
       ${lifeMeta}
     </div>
-    <div class="account-hoster-group-body" ${bodyStyle}>${cardsHtml}</div>
+    <div class="account-hoster-group-body account-collapse${isOpen ? ' is-open' : ''}" aria-hidden="${!isOpen}" ${isOpen ? '' : 'inert'}>
+      <div class="account-collapse-content"><div class="account-hoster-group-body-inner">${cardsHtml}</div></div>
+    </div>
     ${_buildHosterSettingsHtml(name)}
   </div>`;
 }
@@ -5029,18 +5031,25 @@ function _invalidateHosterLifetimeCache() { _hosterLifetimeCache = null; }
 function _allAccountGroupsOpen() {
   const bodies = document.querySelectorAll('#accountsList .account-hoster-group-body');
   if (!bodies.length) return false;
-  for (const b of bodies) if (b.style.display === 'none') return false;
+  for (const body of bodies) if (!body.classList.contains('is-open')) return false;
   return true;
 }
 
+function _setAccountCollapseOpen(trigger, body, open) {
+  if (!body) return;
+  body.classList.toggle('is-open', open);
+  body.setAttribute('aria-hidden', String(!open));
+  body.toggleAttribute('inert', !open);
+  if (trigger) trigger.setAttribute('aria-expanded', String(open));
+}
+
 function _setAllAccountGroupsOpen(open) {
   const groups = document.querySelectorAll('#accountsList .account-hoster-group');
   groups.forEach(group => {
     const name = group.dataset.hosterGroup;
     const body = group.querySelector('.account-hoster-group-body');
-    const arrow = group.querySelector('.panel-arrow');
-    if (body) body.style.display = open ? '' : 'none';
-    if (arrow) arrow.innerHTML = open ? '&#9660;' : '&#9654;';
+    const header = group.querySelector('[data-hoster-toggle]');
+    _setAccountCollapseOpen(header, body, open);
     if (name) {
       const summary = _summarizeHosterGroup(config.hosters[name] || []);
       _hosterGroupOpenMemory.set(name, { state: open ? 'open' : 'closed', errorsAtClose: summary.error });
@@ -5068,11 +5077,9 @@ function bindAccountListeners(container) {
       const name = header.dataset.hosterToggle;
       const group = header.closest('.account-hoster-group');
       const body = group && group.querySelector('.account-hoster-group-body');
-      const arrow = header.querySelector('.panel-arrow');
       if (body) {
-        const willOpen = body.style.display === 'none';
-        body.style.display = willOpen ? '' : 'none';
-        if (arrow) arrow.innerHTML = willOpen ? '&#9660;' : '&#9654;';
+        const willOpen = !body.classList.contains('is-open');
+        _setAccountCollapseOpen(header, body, willOpen);
         const summary = _summarizeHosterGroup(config.hosters[name] || []);
         _hosterGroupOpenMemory.set(name, { state: willOpen ? 'open' : 'closed', errorsAtClose: summary.error });
       }
@@ -5081,11 +5088,9 @@ function bindAccountListeners(container) {
     const settingsHeader = e.target.closest('[data-hoster-settings-toggle]');
     if (settingsHeader) {
       const body = settingsHeader.nextElementSibling;
-      const arrow = settingsHeader.querySelector('.panel-arrow');
       if (body) {
-        const isOpen = body.style.display !== 'none';
-        body.style.display = isOpen ? 'none' : '';
-        if (arrow) arrow.innerHTML = isOpen ? '&#9654;' : '&#9660;';
+        const willOpen = !body.classList.contains('is-open');
+        _setAccountCollapseOpen(settingsHeader, body, willOpen);
       }
       return;
     }
diff --git a/renderer/styles.css b/renderer/styles.css
index f0e3822..78c1348 100644
--- a/renderer/styles.css
+++ b/renderer/styles.css
@@ -1275,7 +1275,7 @@ select.hs-input { max-width: none; width: auto; min-width: 140px; }
 }
 .account-hoster-settings-header:hover { background: var(--bg-card-hover); color: var(--text); }
 .account-hoster-settings-header .panel-arrow { font-size: 10px; color: var(--text-dim); }
-.account-hoster-settings-body { padding: 4px 12px 10px; }
+.account-hoster-settings-body-inner { padding: 4px 12px 10px; }
 
 .settings-hoster-pointer {
   margin-top: 12px;
@@ -1374,7 +1374,7 @@ select.hs-input { max-width: none; width: auto; min-width: 140px; }
 .batch-cat-tag.retryable { background: rgba(76, 175, 80, 0.18); color: #a5d6a7; }
 .batch-cat-list { margin: 0; padding-left: 18px; font-size: 11px; color: var(--text-muted); }
 .batch-cat-list em { color: var(--text-muted); font-style: italic; }
-.account-hoster-group-body {
+.account-hoster-group-body-inner {
   padding: 8px;
   border-top: 1px solid var(--border);
 }
@@ -1392,6 +1392,38 @@ select.hs-input { max-width: none; width: auto; min-width: 140px; }
   display: inline-block;
 }
 
+.account-collapse {
+  display: grid;
+  grid-template-rows: 0fr;
+  opacity: 0;
+  visibility: hidden;
+  transition: grid-template-rows 220ms cubic-bezier(.2, .8, .2, 1), opacity 160ms ease, visibility 0s linear 220ms;
+}
+
+.account-collapse.is-open {
+  grid-template-rows: 1fr;
+  opacity: 1;
+  visibility: visible;
+  transition-delay: 0s;
+}
+
+.account-collapse-content {
+  min-height: 0;
+  overflow: hidden;
+}
+
+.account-hoster-group-header .panel-arrow,
+.account-hoster-settings-header .panel-arrow {
+  display: inline-block;
+  transform-origin: center;
+  transition: transform 180ms cubic-bezier(.2, .8, .2, 1);
+}
+
+.account-hoster-group-header[aria-expanded="true"] .panel-arrow,
+.account-hoster-settings-header[aria-expanded="true"] .panel-arrow {
+  transform: rotate(90deg);
+}
+
 .accounts-empty {
   width: min(520px, 100%);
   margin: clamp(56px, 12vh, 120px) auto 0;
@@ -1716,6 +1748,15 @@ select.hs-input { max-width: none; width: auto; min-width: 140px; }
   .menu-closing {
     animation-duration: 160ms !important;
   }
+
+  .account-collapse {
+    transition-duration: 220ms, 160ms, 0s !important;
+  }
+
+  .account-hoster-group-header .panel-arrow,
+  .account-hoster-settings-header .panel-arrow {
+    transition-duration: 180ms !important;
+  }
 }
 
 .online-backup-panel {
@@ -3186,10 +3227,17 @@ input[type="checkbox"] {
 }
 
 .accounts-auto-check {
-  min-height: 38px;
+  min-height: 34px;
+  height: 34px;
   padding: 0 12px;
   border-radius: 6px;
   background: var(--bg-raised);
+  box-sizing: border-box;
+}
+
+.accounts-header-actions > .btn {
+  min-height: 34px;
+  height: 34px;
 }
 
 .account-health-results {
diff --git a/tests/ui-smoke.js b/tests/ui-smoke.js
index f488497..226a978 100644
--- a/tests/ui-smoke.js
+++ b/tests/ui-smoke.js
@@ -457,6 +457,9 @@ setTimeout(async () => {
     const accountsFrameFit = await wc.executeJavaScript('(() => { const view = document.getElementById("accounts-view")?.getBoundingClientRect(); const status = document.getElementById("statusbar")?.getBoundingClientRect(); return Boolean(view && status && status.height > 0 && view.bottom <= status.top + 1 && status.bottom <= window.innerHeight + 1); })()');
     check('Accounts view and statusbar fit inside the viewport', accountsFrameFit === true);
 
+    const accountHeaderControlHeights = await wc.executeJavaScript('(() => [document.getElementById("accountsRunHealthCheckBtn"), document.querySelector(".accounts-auto-check"), document.getElementById("addAccountBtn")].map(element => element?.getBoundingClientRect().height || 0))()');
+    check('Accounts header actions share one rendered height', accountHeaderControlHeights.every(height => height > 0 && Math.abs(height - accountHeaderControlHeights[0]) <= 0.5));
+
     await captureVisual('02-accounts.png');
 
     const accountListValid = await wc.executeJavaScript('Boolean(document.querySelector("#accountsList .accounts-empty") || document.querySelectorAll("#accountsList .account-hoster-group").length)');
@@ -536,6 +539,39 @@ setTimeout(async () => {
     check('Empty account state remains contained at 1280x720', emptyAccountsGeometry.emptyVisible && emptyAccountsGeometry.contained);
     await captureVisual('02-accounts-empty-1280x720.png');
 
+    const accountCollapseMotion = await wc.executeJavaScript(\`(async () => {
+      const hoster = HOSTERS[0];
+      HOSTERS.forEach(name => { config.hosters[name] = []; });
+      config.hosters[hoster] = [{ id: 'ui-collapse-account', label: 'Animated account', enabled: true, authType: 'login', username: 'animated@example.invalid', password: 'fictional-password' }];
+      accountStatuses = { 'ui-collapse-account': { status: 'ok', message: 'Bereit' } };
+      _hosterGroupOpenMemory.set(hoster, { state: 'closed', errorsAtClose: 0 });
+      renderAccounts();
+      const wait = ms => new Promise(resolve => setTimeout(resolve, ms));
+      const sample = async (trigger, body) => {
+        const closedStart = body.getBoundingClientRect().height;
+        trigger.click();
+        await wait(70);
+        const opening = body.getBoundingClientRect().height;
+        const openingState = body.classList.contains('is-open');
+        const duration = parseFloat(getComputedStyle(body).transitionDuration) * 1000;
+        await wait(240);
+        const opened = body.getBoundingClientRect().height;
+        trigger.click();
+        await wait(70);
+        const closing = body.getBoundingClientRect().height;
+        const closingState = !body.classList.contains('is-open');
+        await wait(240);
+        const closedEnd = body.getBoundingClientRect().height;
+        return { closedStart, opening, opened, closing, closedEnd, openingState, closingState, duration };
+      };
+      const hosterMotion = await sample(document.querySelector('[data-hoster-toggle]'), document.querySelector('.account-hoster-group-body'));
+      const settingsMotion = await sample(document.querySelector('[data-hoster-settings-toggle]'), document.querySelector('.account-hoster-settings-body'));
+      return { hosterMotion, settingsMotion };
+    })()\`);
+    const hasSmoothAccountCollapse = motion => motion.closedStart <= 1 && motion.opening > 1 && motion.opening < motion.opened - 1 && motion.closing > 1 && motion.closing < motion.opened - 1 && motion.closedEnd <= 1 && motion.openingState && motion.closingState && motion.duration >= 180;
+    check('Hoster groups visibly animate while opening and closing', hasSmoothAccountCollapse(accountCollapseMotion.hosterMotion));
+    check('Hoster upload settings visibly animate while opening and closing', hasSmoothAccountCollapse(accountCollapseMotion.settingsMotion));
+
     const tallAccountGroupGeometry = await wc.executeJavaScript(\`(() => {
       const hoster = HOSTERS[0];
       HOSTERS.forEach(name => { config.hosters[name] = []; });
@@ -582,7 +618,7 @@ setTimeout(async () => {
       });
       renderAccounts();
       document.querySelectorAll('[data-hoster-toggle]').forEach(header => {
-        if (header.nextElementSibling?.style.display === 'none') header.click();
+        if (!header.nextElementSibling?.classList.contains('is-open')) header.click();
       });
       [...document.querySelectorAll('[data-hoster-settings-toggle]')].slice(0, 3).forEach(header => header.click());
       const list = document.getElementById('accountsList');
@@ -590,8 +626,8 @@ setTimeout(async () => {
       if (list) list.scrollTop = list.scrollHeight;
       return {
         groupCount: groups.length,
-        openGroupCount: groups.filter(group => group.querySelector('.account-hoster-group-body')?.style.display !== 'none').length,
-        openSettingsCount: groups.filter(group => group.querySelector('.account-hoster-settings-body')?.style.display !== 'none').length,
+        openGroupCount: groups.filter(group => group.querySelector('.account-hoster-group-body')?.classList.contains('is-open')).length,
+        openSettingsCount: groups.filter(group => group.querySelector('.account-hoster-settings-body')?.classList.contains('is-open')).length,
         listClientHeight: list?.clientHeight || 0,
         listScrollHeight: list?.scrollHeight || 0,
         listScrollTop: list?.scrollTop || 0,