Center the header logo

Signed-off-by: Rémy Coutable <remy@rymai.me>

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.13.0 (unreleased)
   - Use gitlab-shell v3.6.2 (GIT TRACE logging)
+  - Fix centering of custom header logos (Ashley Dumaine)
   - AbstractReferenceFilter caches project_refs on RequestStore when active
   - Speed-up group milestones show page
   - Log LDAP lookup errors and don't swallow unrelated exceptions. !6103 (Markus Koller)

app/assets/stylesheets/framework/header.scss

@@ -112,11 +112,15 @@ header {
     .header-logo {
       position: absolute;
       left: 50%;
-      margin-left: -18px;
       top: 7px;
       transition-duration: .3s;
       z-index: 999;
 
+      #logo {
+        position: relative;
+        left: -50%;
+      }
+
       svg, img {
         height: 36px;
       }