diff --git a/data_visualization/css/base.css b/data_visualization/css/base.css
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+/* ============================================
+   Base Styles – Donau Data Visualization
+   ============================================ */
+
+/* ------------------------------
+   Section: root_reset
+   ------------------------------ */
+html, body {
+  margin: 0;
+  padding: 0;
+  height: 100%;
+  width: 100%;
+  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
+  font-size: 16px;
+  line-height: 1.5;
+  background-color: var(--color-bg);
+  color: var(--color-text);
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+*, *::before, *::after {
+  box-sizing: border-box;
+}
+
+main {
+  display: flex;
+  flex-direction: column;
+  min-height: 100vh;
+}
+
+/* ------------------------------
+   Section: variables
+   ------------------------------ */
+:root {
+  /* Farbpalette */
+  --color-bg: #f8f9fa;
+  --color-surface: #ffffff;
+  --color-primary: #005f73;
+  --color-primary-light: #0a9396;
+  --color-secondary: #94d2bd;
+  --color-accent: #ee9b00;
+  --color-text: #222222;
+  --color-text-muted: #555555;
+  --color-border: #dddddd;
+
+  /* Spacing */
+  --spacing-xs: 0.25rem;
+  --spacing-sm: 0.5rem;
+  --spacing-md: 1rem;
+  --spacing-lg: 2rem;
+  --spacing-xl: 4rem;
+
+  /* Typografie */
+  --font-size-base: 1rem;
+  --font-size-lg: 1.25rem;
+  --font-size-xl: 2rem;
+  --font-weight-normal: 400;
+  --font-weight-bold: 600;
+
+  /* Breakpoints */
+  --bp-sm: 640px;
+  --bp-md: 1024px;
+}
+
+/* ------------------------------
+   Section: typography
+   ------------------------------ */
+.app-header {
+  background-color: var(--color-primary);
+  color: var(--color-surface);
+  padding: var(--spacing-md);
+  text-align: center;
+  font-size: var(--font-size-xl);
+  font-weight: var(--font-weight-bold);
+  letter-spacing: 0.05em;
+}
+
+.app-footer {
+  background-color: var(--color-surface);
+  color: var(--color-text-muted);
+  text-align: center;
+  padding: var(--spacing-sm) var(--spacing-md);
+  font-size: 0.875rem;
+  border-top: 1px solid var(--color-border);
+}
+
+.app-footer small {
+  display: block;
+  margin-top: var(--spacing-xs);
+  font-size: 0.75rem;
+}
+
+/* ------------------------------
+   Responsive adjustments
+   ------------------------------ */
+@media (min-width: var(--bp-md)) {
+  .app-header {
+    font-size: calc(var(--font-size-xl) * 1.2);
+    text-align: left;
+    padding: var(--spacing-lg);
+  }
+  .app-footer {
+    font-size: 1rem;
+  }
+}
+
+/* ------------------------------
+   Legal notice
+   ------------------------------ */
+.app-footer::after {
+  content: "© 2026 Donau2Space.de";
+  display: block;
+  margin-top: var(--spacing-xs);
+  font-size: 0.75rem;
+  color: var(--color-text-muted);
+}
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