diff --git a/data_visualization/css/base.css b/data_visualization/css/base.css
new file mode 100644
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+++ b/data_visualization/css/base.css
@@ -0,0 +1,93 @@
+/* ==============================
+   Variables
+   ============================== */
+:root {
+  --color-background: #f8f9fa;
+  --color-surface: #ffffff;
+  --color-text-primary: #1a1a1a;
+  --color-text-secondary: #555555;
+  --color-accent: #006d77;
+  --color-highlight: #ffb703;
+
+  --font-base: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+  --font-size-base: 1rem;
+
+  --spacing-xs: 0.25rem;
+  --spacing-sm: 0.5rem;
+  --spacing-md: 1rem;
+  --spacing-lg: 1.5rem;
+  --spacing-xl: 2rem;
+
+  --radius-sm: 4px;
+  --radius-md: 8px;
+  --transition-fast: 150ms ease-in-out;
+  --max-width-content: 1200px;
+}
+
+/* ==============================
+   Base Reset
+   ============================== */
+html, body {
+  margin: 0;
+  padding: 0;
+  height: 100%;
+  font-family: var(--font-base);
+  font-size: var(--font-size-base);
+  background-color: var(--color-background);
+  color: var(--color-text-primary);
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+*, *::before, *::after {
+  box-sizing: border-box;
+}
+
+a {
+  color: var(--color-accent);
+  text-decoration: none;
+  transition: color var(--transition-fast);
+}
+
+a:hover, a:focus {
+  color: var(--color-highlight);
+}
+
+/* ==============================
+   App Structure
+   ============================== */
+.app-header {
+  background-color: var(--color-surface);
+  padding: var(--spacing-md);
+  border-bottom: 1px solid #ddd;
+}
+
+.app-main {
+  max-width: var(--max-width-content);
+  margin: 0 auto;
+  padding: var(--spacing-md);
+}
+
+.app-footer {
+  text-align: center;
+  padding: var(--spacing-sm);
+  font-size: 0.85rem;
+  color: var(--color-text-secondary);
+  border-top: 1px solid #ddd;
+  background-color: var(--color-surface);
+}
+
+.app-footer::after {
+  content: "© 2026 Donau2Space.de";
+  display: block;
+  margin-top: var(--spacing-xs);
+}
+
+@media (min-width: 640px) {
+  .app-header, .app-footer {
+    padding: var(--spacing-lg);
+  }
+  .app-main {
+    padding: var(--spacing-lg);
+  }
+}
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