Remove parent window (dangling in background) for chrome://settings when invoked at OOBE screen.

chrome/browser/resources/options/options_page.css

 body {
   -webkit-user-select: none;
   cursor: default;
   font-size: 100%;
 }
 
 #settings-title {
   -webkit-padding-end: 24px;
   color: #53637d;
   font-size: 200%;
@@ skipping 49 matching lines @@
 html[dir='ltr'] .close-subpage {
   float: right;
   right: 0;
 }
 
 html[dir='rtl'] .close-subpage {
   float: left;
   left: 0;
 }
 
+html[hide-menu=true] .close-subpage {
+  display: none
+}
+
 .action-area {
   -webkit-box-orient: horizontal;
   -webkit-box-align: center;
   padding: 12px;
   position: absolute;
   right: 0px;
   bottom: 0px;
   display: -webkit-box;
 }
 
@@ skipping 402 matching lines @@
 label.radio > span,
 .suboption {
   -webkit-margin-start: 16px;
   display: block;
 }
 
 html[os=mac] label.checkbox > input,
 html[os=mac] label.radio > input {
   margin-top: 2px;
 }