update logo (#35)

Author: Arhell

docs/assets/css/extra.css

@@ -14,3 +14,10 @@
 [data-md-color-scheme="slate"] .md-nav__link:hover {
     color: #699cfa !important;
 }
+
+.md-header__button.md-logo {
+    background-color: #ffffff;
+    border-radius: 2px;
+    margin-top: 10px;
+    padding: .25rem !important;
+}