refactor: Reduce duplicated code

- move categorical navigation menu HTMLinto category-nav.njk and CSS into category-nav.css

src/index.njk

@@ -8,6 +8,7 @@ stylesheet:
     - "/styles/base.css"
     - "/styles/header.css"
     - "/styles/index.css"
+    - "/styles/category-nav.css"
     - "/styles/footer.css"
     - "/styles/modal.css"
 fontAwesome: "https://kit.fontawesome.com/c42448086d.js"
@@ -70,22 +71,6 @@ pageScripts:
 		</section>
 	</div>
 
-	<div id="right-side">
-		<nav id="category-nav">
-			<div id="category-nav-container">
-				<h2>Shop by Category</h2>
-				<div class="categories">
-					<ul>
-						<li><a href="/gallery/?category=trees#" class="cat-btn">Trees</a></li>
-						<li><a href="/gallery/?category=shrubs#" class="cat-btn">Shrubs</a></li>
-						<li><a href="/gallery/?category=indoor#" class="cat-btn">Indoor</a></li>
-						<li><a href="/gallery/?category=patio#" class="cat-btn">Patio</a></li>
-						<li><a href="/gallery/?category=tools#" class="cat-btn">Tools</a></li>
-						<li><a href="/gallery/?category=accessories#" class="cat-btn">Accessories</a></li>
-						<li><a href="/gallery/?category=landscaping#" class="cat-btn">Landscaping</a></li>
-					</ul>
-				</div>
-			</div>
-		</nav>
-	</div>
+	{% include "category-nav.njk" %}
+	
 </div>