Add App CSS styles

client/src/App.css

@@ -0,0 +1,79 @@
+.app {
+  min-height: 100vh;
+  display: flex;
+  flex-direction: column;
+}
+
+.navbar {
+  background: var(--bg);
+  box-shadow: var(--shadow);
+  position: sticky;
+  top: 0;
+  z-index: 100;
+}
+
+.navbar .container {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 1rem;
+}
+
+.nav-brand {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  color: var(--primary);
+  font-weight: 700;
+  font-size: 1.5rem;
+}
+
+.brand-text {
+  letter-spacing: 0.05em;
+}
+
+.nav-links {
+  display: flex;
+  gap: 0.5rem;
+}
+
+.nav-link {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  padding: 0.625rem 1rem;
+  border-radius: 0.375rem;
+  color: var(--text-secondary);
+  text-decoration: none;
+  font-weight: 500;
+  transition: all 0.2s;
+}
+
+.nav-link:hover {
+  background: var(--bg-secondary);
+  color: var(--primary);
+}
+
+.nav-link.active {
+  background: var(--primary);
+  color: white;
+}
+
+.main-content {
+  flex: 1;
+  padding: 2rem 0;
+}
+
+@media (max-width: 768px) {
+  .nav-links {
+    gap: 0.25rem;
+  }
+  
+  .nav-link span {
+    display: none;
+  }
+  
+  .nav-link {
+    padding: 0.625rem;
+  }
+}