Add header

style.css

@@ -64,4 +64,35 @@ h1 {
 
 #history_gallery img:hover {
     transform: scale(1.05);
+}
+
+header {
+    background-color: #222;
+    padding: 20px;
+    position: sticky;
+    top: 0;
+    z-index: 100;
+}
+
+nav {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+}
+
+nav img {
+    height: 40px;
+}
+
+.mode-switch {
+    display: flex;
+    gap: 10px;
+    background-color: #FAF0E6; /* Pearl white background color */
+    padding: 10px;
+    border-radius: 5px;
+}
+
+.mode-switch img {
+    cursor: pointer;
+    height: 24px;
 }