diff --git a/data_visualization/css/base.css b/data_visualization/css/base.css
new file mode 100644
index 0000000..0140429
--- /dev/null
+++ b/data_visualization/css/base.css
@@ -0,0 +1,100 @@
+/* =========================================
+   CSS Reset & Root Variables
+   ========================================= */
+
+:root {
+  --color-bg: #f9fafb;
+  --color-text: #222222;
+  --color-accent: #0066cc;
+  --color-muted: #6b7280;
+  --spacing-xs: 0.25rem;
+  --spacing-sm: 0.5rem;
+  --spacing-md: 1rem;
+  --spacing-lg: 2rem;
+  --font-base: 'Arial', sans-serif;
+  --font-size-base: 16px;
+  --max-width: 1200px;
+  --breakpoint-sm: 640px;
+  --breakpoint-md: 1024px;
+}
+
+/* CSS Reset */
+
+*, *::before, *::after {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+html {
+  font-size: 100%;
+  scroll-behavior: smooth;
+}
+
+body {
+  font-family: var(--font-base);
+  font-size: var(--font-size-base);
+  background-color: var(--color-bg);
+  color: var(--color-text);
+  line-height: 1.5;
+  min-height: 100vh;
+  display: flex;
+  flex-direction: column;
+}
+
+/* =========================================
+   App Shell Layout
+   ========================================= */
+
+.app-header {
+  background-color: #ffffff;
+  border-bottom: 1px solid #e5e7eb;
+  padding: var(--spacing-md);
+  text-align: center;
+  font-weight: bold;
+}
+
+.app-main {
+  flex: 1;
+  width: 100%;
+  max-width: var(--max-width);
+  margin: 0 auto;
+  padding: var(--spacing-md);
+}
+
+.app-footer {
+  background-color: #ffffff;
+  border-top: 1px solid #e5e7eb;
+  text-align: center;
+  padding: var(--spacing-sm);
+  font-size: 0.875rem;
+  color: var(--color-muted);
+}
+
+.app-footer::after {
+  content: '© 2026 Donau2Space.de';
+  display: block;
+  margin-top: var(--spacing-xs);
+}
+
+/* =========================================
+   Responsive Adjustments
+   ========================================= */
+
+@media (min-width: var(--breakpoint-sm)) {
+  .app-header {
+    text-align: left;
+    padding: var(--spacing-lg);
+  }
+
+  .app-main {
+    padding: var(--spacing-lg);
+  }
+}
+
+@media (min-width: var(--breakpoint-md)) {
+  .app-header,
+  .app-footer {
+    padding: var(--spacing-lg) var(--spacing-md);
+  }
+}