docs: add custom head

Author: itsjavi

_includes/head-custom.html

@@ -0,0 +1,25 @@
+<style>
+    html, body {
+        color: #fafafa;
+        background-color: #252525;
+    }
+
+    .markdown-body img {
+      background-color: transparent;
+    }
+
+    .markdown-body h1, 
+    .markdown-body h2, 
+    .markdown-body h3, 
+    .markdown-body p {
+      border-bottom-color: #555555;
+    }
+
+    .highlight {
+      background-color: transparent;
+    }
+    .markdown-body .highlight pre, .markdown-body pre {
+      background-color: #333333;
+    }
+</style>
+