make header optionnal

lib/html_body.typ

@@ -6,7 +6,7 @@
 /// Make the body of the webpage
 #let html_body(
   /// The visible header of the page
-  header: [],
+  header: none,
   /// Logo of the site
   logo: none,
   /// Navigation menu content, css style expect a list
@@ -72,16 +72,14 @@
         if menu != none {
           nav-menu(menu)
         }
-        html.header(style: "display: flex; flex-wrap: wrap-reverse;", {
-          html.hgroup({
-            header
-          })
-          // typst `image` function embed the image in the html, which is not great,
-          // and logo is also used for icon, so it's necessarily an url
-          if logo != none {
+        if header != none or logo != none {
+          html.header(style: "display: flex; flex-wrap: wrap-reverse;", {
+            html.hgroup({
+              header
+            })
             logo
-          }
-        })
+          })
+        }
         body
       })
     })