Redesign homepage layout and update content

Align homepage content to center, adjust sidebar width and page
max-width, update hero text to Chinese, and apply dark background
for the site.

assets/css/custom.css

@@ -28,3 +28,27 @@ kbd {
 .hextra-nav-container-blur {
     box-shadow: none !important;
 }
+
+/* Shift logo left to compensate for internal whitespace */
+nav a:first-of-type img {
+    margin-left: -10px;
+}
+
+/* Unified widths — all sections aligned at 76rem */
+:root {
+    --hx-color-dark: #000;
+    --hextra-max-page-width: 76rem;
+    --hextra-max-content-width: 76rem;
+    --hextra-max-navbar-width: 76rem;
+    --hextra-max-footer-width: 76rem;
+}
+
+/* Narrow left sidebar to half width (128px) */
+.hextra-sidebar-container {
+    width: 8rem !important;
+}
+
+.dark body,
+body:where(.dark) {
+    background-color: #000;
+}