Make the width of overlay pages flexible.

chrome/browser/resources/options/options_page.css

 #settings-title {
   height: 30px;
   -webkit-padding-end: 15px;
   padding-top: 20px;
   text-align: end;
   font-size: 140%;
   color: #c7c7c7;
 }
 
 #main-content {
   display: -webkit-box;
   position: absolute;
   left: 0;
   right: 0;
   top: 0;
   bottom: 0;
 }
 
 .overlay {
   position: fixed;
   left: 0;
   right: 0;
   background: rgba(0, 0, 0, .5);
   top: 0;
   bottom: 0;
   z-index: 10;
   padding: 20px;
+  display: -webkit-box;
+  -webkit-box-align: start;
+  -webkit-box-pack: center;
 }
 
 #close-overlay {
   position: relative;
   top: -20px;
   width: 20px;
   height: 20px;
 }
 
 html[dir='ltr'] #close-overlay {
   float: right;
   right: -20px;
 }
 
 html[dir='rtl'] #close-overlay {
   float: left;
   left: -20px;
 }
 
-#overlayview .button-strip {
+.overlay .button-strip {
   text-align: end;
 }
 
-#overlayview {
+.overlay > div {
   background: white;
   border-radius: 5px;
   padding: 30px;
 }
 
 #navbar-container {
   background: -webkit-gradient(linear,
                                left top,
                                left bottom,
                                from(rgba(255,255,255,0)),
@@ skipping 111 matching lines @@
   display: none;
 }
 
 .touch-slider {
   -webkit-appearance: slider-horizontal;
 }
 
 input[type="checkbox"] {
   margin-top: 6px;
 }