Add optional navbar search (for docs.gitea.io) (#112)

Reviewed-on: https://gitea.com/gitea/theme/pulls/112
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: John Olheiser <john+gitea@jolheiser.com>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

src/main.scss

@@ -58,6 +58,18 @@
   }
 }
 
+.navbar .navbar-brand {
+  align-items: center;
+  justify-content: space-between;
+  flex-grow: 1;
+  input {
+    height: 50%;
+    padding: 0.3rem;
+    margin-right: 0.75rem;
+  }
+}
+
+
 // Mobile Styles
 
 .navbar {
@@ -77,6 +89,10 @@
 }
 
 @media screen and (max-width:1023px){
+  .navbar .navbar-brand {
+    justify-content: initial;
+  }
+
   .navbar-menu{
     position: fixed;
     bottom: 0;