style: add Code with Branko branding and custom CSS

Add extra.css for banner styling, card hover effects, and
consistent brand appearance. Reference custom stylesheet in config.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: braboj

docs/stylesheets/extra.css

@@ -0,0 +1,21 @@
+/* Code with Branko — Git Tutorial custom styles */
+
+/* Hero banner on landing page */
+.md-content img[alt="Banner"] {
+  display: block;
+  margin: 0 auto 1.5rem;
+  max-width: 600px;
+  border-radius: 8px;
+}
+
+/* Card grid styling for landing page */
+.md-typeset .grid.cards > ul > li {
+  border: 1px solid var(--md-default-fg-color--lightest);
+  border-radius: 8px;
+  transition: border-color 0.2s, box-shadow 0.2s;
+}
+
+.md-typeset .grid.cards > ul > li:hover {
+  border-color: var(--md-accent-fg-color);
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
+}

mkdocs.yml

@@ -68,6 +68,9 @@ extra:
 
 copyright: "© 2021–2026 Branimir Georgiev · Code with Branko"
 
+extra_css:
+  - stylesheets/extra.css
+
 nav:
   - Home:
     - index.md