diff --git a/.beads/issues.jsonl b/.beads/issues.jsonl
index 5fd6b74..7742e2e 100644
--- a/.beads/issues.jsonl
+++ b/.beads/issues.jsonl
@@ -1,11 +1,11 @@
-{"id":"books-1rp","title":"http://localhost:3000/kunder","status":"open","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:30:29.369137+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:30:29.369137+01:00"}
+{"id":"books-1rp","title":"http://localhost:3000/kunder","status":"in_progress","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:30:29.369137+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:45:00.573047+01:00"}
 {"id":"books-5tg","title":"opret et backend job med hangfir\ne som sikrer, at bankkonto altid stemmer med den pågældende konto","status":"closed","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:24:01.505911+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:37:08.293897+01:00","closed_at":"2026-01-30T14:37:08.293897+01:00","close_reason":"Closed"}
 {"id":"books-8ea","title":"fjern brugers navn fra højre hjørne ved profile ikonet","status":"closed","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:20:16.406033+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:22:59.64468+01:00","closed_at":"2026-01-30T14:22:59.64468+01:00","close_reason":"Closed"}
-{"id":"books-8lo","title":"revisit the laytoug and desig nfor kontooversigten.","status":"open","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:25:06.620288+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:25:06.620288+01:00"}
+{"id":"books-8lo","title":"revisit the laytoug and desig nfor kontooversigten.","status":"in_progress","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:25:06.620288+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:45:00.448995+01:00"}
 {"id":"books-bj6","title":"Test automatisk pickup","status":"closed","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:04:40.572496+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:05:44.401903+01:00","closed_at":"2026-01-30T14:05:44.401903+01:00","close_reason":"completed"}
 {"id":"books-byl","title":"opret giv et shortlink på frontenden til backend på /hangfire","status":"closed","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:24:34.946139+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:40:44.62014+01:00","closed_at":"2026-01-30T14:40:44.62014+01:00","close_reason":"Closed"}
 {"id":"books-cdf","title":"opret","status":"open","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:23:39.411558+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:23:39.411558+01:00"}
-{"id":"books-ced","title":"brug smb om regnskab + fropntend designer til at sikrer at alt er godt for både balance og kontooversigt","status":"open","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:25:46.484629+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:25:46.484629+01:00"}
+{"id":"books-ced","title":"brug smb om regnskab + fropntend designer til at sikrer at alt er godt for både balance og kontooversigt","status":"in_progress","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:25:46.484629+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:45:00.511206+01:00"}
 {"id":"books-h6e","title":"fjern hurtig bogføring og den visning der høre dertil","status":"closed","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:14:50.436314+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:18:09.911294+01:00","closed_at":"2026-01-30T14:18:09.911294+01:00","close_reason":"Closed"}
 {"id":"books-hzt","title":"fix bug med tilføj brugere står forkert med encoded tegn","status":"closed","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:21:34.556319+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:28:31.320973+01:00","closed_at":"2026-01-30T14:28:31.320973+01:00","close_reason":"Closed"}
 {"id":"books-sbm","title":"ændre navnet i venstre side til Books","status":"closed","priority":2,"issue_type":"task","owner":"nhh@softwarehuset.com","created_at":"2026-01-30T14:11:13.017202+01:00","created_by":"Nicolaj Hartmann","updated_at":"2026-01-30T14:12:14.16594+01:00","closed_at":"2026-01-30T14:12:14.16594+01:00","close_reason":"Closed"}
diff --git a/frontend/src/lib/formatters.ts b/frontend/src/lib/formatters.ts
index 442e86e..3be1bf2 100644
--- a/frontend/src/lib/formatters.ts
+++ b/frontend/src/lib/formatters.ts
@@ -112,6 +112,28 @@ export function formatCVR(cvr: string): string {
   return `${cleaned.slice(0, 2)} ${cleaned.slice(2, 4)} ${cleaned.slice(4, 6)} ${cleaned.slice(6, 8)}`;
 }
 
+/**
+ * Validate a Danish CVR number using the modulus 11 algorithm
+ * @param cvr - 8-digit CVR number as string
+ * @returns true if valid, false otherwise
+ */
+export function validateCVRModulus11(cvr: string): boolean {
+  const cleaned = cvr.replace(/\D/g, '');
+  if (cleaned.length !== 8) return false;
+
+  // Weights for each position in the CVR number
+  const weights = [2, 7, 6, 5, 4, 3, 2, 1];
+
+  // Calculate weighted sum
+  let sum = 0;
+  for (let i = 0; i < 8; i++) {
+    sum += parseInt(cleaned[i], 10) * weights[i];
+  }
+
+  // Valid if sum is divisible by 11
+  return sum % 11 === 0;
+}
+
 /**
  * Get CSS class for amount (positive/negative/zero)
  */
diff --git a/frontend/src/pages/Kontooversigt.tsx b/frontend/src/pages/Kontooversigt.tsx
index fef9821..a6d9a38 100644
--- a/frontend/src/pages/Kontooversigt.tsx
+++ b/frontend/src/pages/Kontooversigt.tsx
@@ -16,6 +16,7 @@ import {
   Tabs,
   Statistic,
   message,
+  Grid,
 } from 'antd';
 import {
   PlusOutlined,
@@ -29,9 +30,13 @@ import { useCompany } from '@/hooks/useCompany';
 import { formatCurrency, formatDate } from '@/lib/formatters';
 import { getAccountTypeName, getAccountNumberRange } from '@/lib/accounting';
 import { accountingColors } from '@/styles/theme';
+import { spacing } from '@/styles/designTokens';
+import { PageHeader } from '@/components/shared/PageHeader';
+import { EmptyState } from '@/components/shared/EmptyState';
 import type { Account, AccountType } from '@/types/accounting';
 
-const { Title, Text } = Typography;
+const { Text } = Typography;
+const { useBreakpoint } = Grid;
 
 // Mock data
 const mockAccounts: Account[] = [
@@ -71,12 +76,15 @@ const accountTypes: AccountType[] = [
 
 export default function Kontooversigt() {
   const { company } = useCompany();
+  const screens = useBreakpoint();
   const [selectedAccount, setSelectedAccount] = useState<Account | null>(null);
   const [isModalOpen, setIsModalOpen] = useState(false);
   const [editingAccount, setEditingAccount] = useState<Account | null>(null);
   const [searchText, setSearchText] = useState('');
   const [form] = Form.useForm();
 
+  const isMobile = !screens.md;
+
   // Build tree data from accounts
   const buildTreeData = (): DataNode[] => {
     return accountTypes.map((type) => {
@@ -235,29 +243,29 @@ export default function Kontooversigt() {
   return (
     <div>
       {/* Header */}
-      <div
-        style={{
-          display: 'flex',
-          justifyContent: 'space-between',
-          alignItems: 'center',
-          marginBottom: 16,
-        }}
-      >
-        <div>
-          <Title level={4} style={{ margin: 0 }}>
-            Kontooversigt
-          </Title>
-          <Text type="secondary">{company?.name}</Text>
-        </div>
-        <Button type="primary" icon={<PlusOutlined />} onClick={handleCreateAccount}>
-          Ny konto
-        </Button>
-      </div>
+      <PageHeader
+        title="Kontooversigt"
+        subtitle={company?.name}
+        breadcrumbs={[
+          { title: 'Bogforing', path: '/bogforing' },
+          { title: 'Kontooversigt' },
+        ]}
+        extra={
+          <Button
+            type="primary"
+            icon={<PlusOutlined />}
+            onClick={handleCreateAccount}
+            aria-label="Opret ny konto"
+          >
+            Ny konto
+          </Button>
+        }
+      />
 
       {/* Summary Cards */}
-      <Row gutter={[16, 16]} style={{ marginBottom: 16 }}>
+      <Row gutter={[spacing.lg, spacing.lg]} style={{ marginBottom: spacing.lg }}>
         <Col xs={12} sm={6}>
-          <Card size="small">
+          <Card size="small" role="region" aria-label="Aktiver total">
             <Statistic
               title="Aktiver"
               value={totalAssets}
@@ -269,7 +277,7 @@ export default function Kontooversigt() {
           </Card>
         </Col>
         <Col xs={12} sm={6}>
-          <Card size="small">
+          <Card size="small" role="region" aria-label="Passiver total">
             <Statistic
               title="Passiver"
               value={totalLiabilities}
@@ -281,9 +289,9 @@ export default function Kontooversigt() {
           </Card>
         </Col>
         <Col xs={12} sm={6}>
-          <Card size="small">
+          <Card size="small" role="region" aria-label="Omsaetning total">
             <Statistic
-              title="Omsætning"
+              title="Omsaetning"
               value={totalRevenue}
               precision={2}
               suffix="kr."
@@ -293,7 +301,7 @@ export default function Kontooversigt() {
           </Card>
         </Col>
         <Col xs={12} sm={6}>
-          <Card size="small">
+          <Card size="small" role="region" aria-label="Omkostninger total">
             <Statistic
               title="Omkostninger"
               value={totalExpenses}
@@ -307,30 +315,31 @@ export default function Kontooversigt() {
       </Row>
 
       {/* Main Content */}
-      <Row gutter={16}>
+      <Row gutter={spacing.lg}>
         {/* Account Tree */}
         <Col xs={24} lg={10}>
-          <Card
-            title="Kontoplan"
-            size="small"
-            extra={
-              <Input
-                placeholder="Søg konto..."
-                prefix={<SearchOutlined />}
-                value={searchText}
-                onChange={(e) => setSearchText(e.target.value)}
-                style={{ width: 200 }}
-                allowClear
-              />
-            }
-          >
+          <Card title="Kontoplan" size="small">
+            {/* Search moved outside extra for better mobile UX */}
+            <Input
+              placeholder="Sog efter konto eller kontonummer..."
+              prefix={<SearchOutlined />}
+              value={searchText}
+              onChange={(e) => setSearchText(e.target.value)}
+              style={{ marginBottom: spacing.md }}
+              allowClear
+              aria-label="Sog i kontoplan"
+            />
             <Tree
               showIcon
               defaultExpandAll
               treeData={buildTreeData()}
               onSelect={handleSelectAccount}
               selectedKeys={selectedAccount ? [selectedAccount.id] : []}
-              style={{ maxHeight: 500, overflow: 'auto' }}
+              style={{
+                maxHeight: isMobile ? 300 : 450,
+                overflow: 'auto',
+              }}
+              aria-label="Kontoplan hierarki"
             />
           </Card>
         </Col>
@@ -343,6 +352,9 @@ export default function Kontooversigt() {
                 <Space>
                   <Text code>{selectedAccount.accountNumber}</Text>
                   <Text strong>{selectedAccount.name}</Text>
+                  {!selectedAccount.isActive && (
+                    <Tag color="red">Inaktiv</Tag>
+                  )}
                 </Space>
               }
               size="small"
@@ -350,10 +362,13 @@ export default function Kontooversigt() {
                 <Button
                   icon={<EditOutlined />}
                   onClick={() => handleEditAccount(selectedAccount)}
+                  aria-label={`Rediger konto ${selectedAccount.accountNumber}`}
                 >
                   Rediger
                 </Button>
               }
+              role="region"
+              aria-label={`Detaljer for konto ${selectedAccount.accountNumber}`}
             >
               <Tabs
                 items={[
@@ -388,6 +403,7 @@ export default function Kontooversigt() {
                           rowKey={(_, index) => String(index)}
                           size="small"
                           pagination={{ pageSize: 10 }}
+                          aria-label={`Bevaegelser for konto ${selectedAccount?.accountNumber}`}
                         />
                       </div>
                     ),
@@ -435,16 +451,13 @@ export default function Kontooversigt() {
             </Card>
           ) : (
             <Card size="small">
-              <div
-                style={{
-                  textAlign: 'center',
-                  padding: 40,
-                  color: '#8c8c8c',
-                }}
-              >
-                <FileOutlined style={{ fontSize: 48, marginBottom: 16 }} />
-                <div>Vælg en konto for at se detaljer</div>
-              </div>
+              <EmptyState
+                variant="accounts"
+                icon={<FileOutlined style={{ fontSize: 48 }} />}
+                title="Ingen konto valgt"
+                description="Vaelg en konto i kontoplanen til venstre for at se detaljer og bevaegelser."
+                compact
+              />
             </Card>
           )}
         </Col>