Introduce CSS variables for consistent theming

This commit refactors existing styles to use CSS variables, centralizing values for colors, spacing, typography, and other design elements. It also adds a `variables.css` file for managing these variables. Updated affected components and stylesheets for better maintainability and consistency.

Gallus_Pub_v1/styles/variables.css

@@ -0,0 +1,30 @@
+:root {
+  /* Colors */
+  --color-background: #000;
+  --color-text: #f5f5f5;
+  --color-accent-green: #213b28;
+  --color-accent-beige: #ceb39b;
+  --color-accent-green-transparent: rgba(33, 59, 40, 0.95);
+  --color-shadow: rgba(0, 0, 0, 0.2);
+
+  --font-family-primary: 'Georgia', serif;
+  --font-size-small: 1rem;
+  --font-size-medium: 1.5rem;
+  --font-size-large: 2rem;
+  --line-height: 1.6;
+
+  --container-width: 100%;
+  --container-max-width: 1600px;
+  --padding-vertical: 2rem;
+  --padding-horizontal: 0;
+  --margin-standard: 1rem;
+  --gap-standard: 30px;
+
+  --border-radius: 8px;
+  --box-shadow: 0 4px 8px var(--color-shadow);
+  --transition-standard: 0.3s ease;
+
+
+  --breakpoint-mobile: 768px;
+  --breakpoint-desktop: 1600px;
+}