diff --git a/data_visualization/css/base.css b/data_visualization/css/base.css
new file mode 100644
index 0000000..fcaf928
--- /dev/null
+++ b/data_visualization/css/base.css
@@ -0,0 +1,69 @@
+:root {
+  --color-bg: #0d0d0d;
+  --color-surface: #1a1a1a;
+  --color-text: #e0e0e0;
+  --color-accent: #4fc3f7;
+  --color-border: #333;
+  --font-base: 'Segoe UI', Roboto, sans-serif;
+  --font-size-base: 16px;
+  --spacing-xs: 0.25rem;
+  --spacing-sm: 0.5rem;
+  --spacing-md: 1rem;
+  --spacing-lg: 2rem;
+  --spacing-xl: 3rem;
+  --max-content-width: 1200px;
+}
+
+/* Reset and base styles */
+*, *::before, *::after {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+html {
+  font-size: 100%;
+  scroll-behavior: smooth;
+}
+
+body {
+  background-color: var(--color-bg);
+  color: var(--color-text);
+  font-family: var(--font-base);
+  font-size: var(--font-size-base);
+  line-height: 1.5;
+  min-height: 100vh;
+  display: flex;
+  flex-direction: column;
+}
+
+/* App layout */
+.app-header {
+  background-color: var(--color-surface);
+  color: var(--color-accent);
+  padding: var(--spacing-md);
+  border-bottom: 1px solid var(--color-border);
+  text-align: center;
+  font-weight: 500;
+}
+
+.app-footer {
+  background-color: var(--color-surface);
+  color: var(--color-text);
+  padding: var(--spacing-sm);
+  border-top: 1px solid var(--color-border);
+  text-align: center;
+  font-size: 0.875rem;
+  margin-top: auto;
+}
+
+.app-footer small {
+  display: block;
+  opacity: 0.75;
+}
+
+@media (min-width: 640px) {
+  .app-header, .app-footer {
+    padding: var(--spacing-lg);
+  }
+}