[FIX] website: Fix modal dialog overlap with navbar

Currently, when there is modal dialog in website the header part of
the modal is hidden behind the navbar and the modal is not centered.

so in this commit, When the modal is in #wrapwrap, modal position
top should be size of the navbar.

closes odoo/odoo#56056

Taskid: 2320303
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/website/static/src/scss/website.scss

@@ -87,6 +87,11 @@ $-seen-urls: ();
 }
 
 #wrapwrap {
+    // When the modal is in #wrapwrap, position top should be size of the navbar
+    .modal {
+        top: $o-navbar-height;
+    }
+
     @if o-website-value('body-image') {
         background-image: url("/#{str-slice(o-website-value('body-image'), 2)}");
         background-position: center;