diff --git a/visualization_tool/css/base.css b/visualization_tool/css/base.css
new file mode 100644
index 0000000..af491d6
--- /dev/null
+++ b/visualization_tool/css/base.css
@@ -0,0 +1,126 @@
+/* ============================
+   Reset und Variablen
+============================ */
+
+*, *::before, *::after {
+  box-sizing: border-box;
+  margin: 0;
+  padding: 0;
+}
+
+html {
+  font-size: 16px;
+  -webkit-text-size-adjust: 100%;
+  scroll-behavior: smooth;
+}
+
+body {
+  font-family: var(--font-base);
+  color: var(--color-text);
+  background-color: var(--color-bg);
+  line-height: 1.5;
+  min-height: 100vh;
+  display: flex;
+  flex-direction: column;
+}
+
+:root {
+  /* Farbvariablen */
+  --color-bg: #f9f9fa;
+  --color-surface: #ffffff;
+  --color-primary: #2d6cdf;
+  --color-accent: #21978d;
+  --color-text: #1b1b1b;
+  --color-muted: #6b7280;
+  --color-border: #d1d5db;
+
+  /* Raumvariablen */
+  --spacing-xs: 0.25rem;
+  --spacing-sm: 0.5rem;
+  --spacing-md: 1rem;
+  --spacing-lg: 1.5rem;
+  --spacing-xl: 2rem;
+
+  /* Schriftvariablen */
+  --font-base: 'Segoe UI', Roboto, sans-serif;
+  --font-size-sm: 0.875rem;
+  --font-size-md: 1rem;
+  --font-size-lg: 1.25rem;
+  --font-size-xl: 1.5rem;
+
+  /* Layoutvariablen */
+  --max-content-width: 1280px;
+  --header-height: 3.5rem;
+  --sidebar-width: 16rem;
+
+  /* Breakpoints */
+  --bp-md: 640px;
+  --bp-lg: 1024px;
+}
+
+/* ============================
+   Grundlayout
+============================ */
+
+.app-shell {
+  display: flex;
+  flex-direction: column;
+  min-height: 100vh;
+}
+
+.app-header {
+  height: var(--header-height);
+  background-color: var(--color-surface);
+  border-bottom: 1px solid var(--color-border);
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 0 var(--spacing-md);
+  font-weight: 600;
+}
+
+.app-main {
+  flex: 1;
+  display: flex;
+  flex-direction: row;
+  max-width: var(--max-content-width);
+  width: 100%;
+  margin: 0 auto;
+  background-color: var(--color-bg);
+}
+
+.app-sidebar {
+  width: var(--sidebar-width);
+  background-color: var(--color-surface);
+  border-right: 1px solid var(--color-border);
+  padding: var(--spacing-md);
+}
+
+.app-footer {
+  background-color: var(--color-surface);
+  border-top: 1px solid var(--color-border);
+  text-align: center;
+  font-size: var(--font-size-sm);
+  color: var(--color-muted);
+  padding: var(--spacing-sm);
+}
+
+/* Responsives Layout */
+
+@media (max-width: var(--bp-md)) {
+  .app-main {
+    flex-direction: column;
+  }
+  .app-sidebar {
+    width: 100%;
+    border-right: none;
+    border-bottom: 1px solid var(--color-border);
+  }
+}
+
+/* Footer Copyright */
+.app-footer::after {
+  content: "© 2026 Donau2Space.de";
+  display: block;
+  margin-top: var(--spacing-xs);
+}
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