diff --git a/heatmap_visualization/css/base.css b/heatmap_visualization/css/base.css
new file mode 100644
index 0000000..e0b711b
--- /dev/null
+++ b/heatmap_visualization/css/base.css
@@ -0,0 +1,124 @@
+/* ===============================
+   Global Base
+   =============================== */
+html, body {
+  margin: 0;
+  padding: 0;
+  width: 100%;
+  height: 100%;
+  box-sizing: border-box;
+  font-family: var(--font-base);
+  background-color: var(--color-bg);
+  color: var(--color-text);
+}
+
+*, *::before, *::after {
+  box-sizing: inherit;
+}
+
+body {
+  display: flex;
+  flex-direction: column;
+  min-height: 100vh;
+}
+
+/* ===============================
+   Variables
+   =============================== */
+:root {
+  --color-bg: #f6f7fb;
+  --color-surface: #ffffff;
+  --color-text: #1b1b1b;
+  --color-accent: #0055cc;
+  --color-border: #d0d7de;
+  --color-legend-low: #e0efff;
+  --color-legend-high: #002b80;
+
+  --font-base: system-ui, sans-serif;
+  --font-size-base: 1rem;
+  --line-height-base: 1.5;
+
+  --spacing-xs: 0.25rem;
+  --spacing-sm: 0.5rem;
+  --spacing-md: 1rem;
+  --spacing-lg: 2rem;
+
+  --radius-sm: 4px;
+  --radius-md: 8px;
+  --shadow-sm: 0 1px 2px rgba(0,0,0,0.1);
+
+  --transition-fast: 0.2s ease;
+  --transition-normal: 0.3s ease;
+
+  --breakpoint-sm: 640px;
+  --breakpoint-md: 1024px;
+}
+
+/* ===============================
+   Layout Containers
+   =============================== */
+.app-header {
+  background-color: var(--color-surface);
+  border-bottom: 1px solid var(--color-border);
+  padding: var(--spacing-md);
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+}
+
+.app-controls {
+  background-color: var(--color-surface);
+  padding: var(--spacing-md);
+  border-bottom: 1px solid var(--color-border);
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--spacing-sm);
+}
+
+.heatmap-area {
+  flex: 1;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background-color: var(--color-bg);
+  padding: var(--spacing-md);
+  overflow: auto;
+}
+
+.heatmap-legend {
+  background-color: var(--color-surface);
+  border-top: 1px solid var(--color-border);
+  padding: var(--spacing-md);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.app-footer {
+  background-color: var(--color-surface);
+  border-top: 1px solid var(--color-border);
+  padding: var(--spacing-sm) var(--spacing-md);
+  text-align: center;
+  font-size: 0.875rem;
+  color: var(--color-text);
+}
+
+@media (min-width: 640px) {
+  .app-controls {
+    justify-content: flex-start;
+  }
+}
+
+@media (min-width: 1024px) {
+  .heatmap-area {
+    padding: var(--spacing-lg);
+  }
+}
+
+.app-footer::after {
+  content: "© 2026 Donau2Space.de";
+  display: block;
+  margin-top: var(--spacing-xs);
+  font-size: 0.75rem;
+  color: var(--color-text);
+}
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