chrome/renderer/resources/plugin_placeholders.css

/* Copyright (c) 2012 The Chromium Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file. */

body {
  font-family: sans-serif;
  margin: 0;
  overflow: hidden;
  text-align: center;
  -webkit-user-select: none;
}

h1 {
  font-size: 10pt;
  font-weight: normal;
  padding: 0pt 10pt;
<if expr="not is_android and not chromeos">
  visibility: hidden;
</if>
}

#outer:hover h1, #outer:hover #close {
  visibility: visible;
}

p {
  font-size: 8pt;
  padding: 0pt 14pt;
}

#outer {
  border: 1px black solid;
  box-sizing: border-box;
  height: 100%;
  position: absolute;
  width: 100%;
}

#inner {
  position: relative;
  height: 100%;
  width: 100%;
  top: 50%;
<if expr="not is_android">
  margin-top: -70px;
</if>
<if expr="is_android">
  margin-top: -14px;
</if>
}

#close {
<if expr="not is_android">
  visibility: hidden;
</if>
  cursor: pointer;
  position: absolute;
  right: 3px;
  top: 3px;
  height: 14px;
  width: 14px;
  background-image: -webkit-image-set(
      url('../../../ui/resources/default_100_percent/close_2.png') 1x,
      url('../../../ui/resources/default_200_percent/close_2.png') 2x);
  background-position: right top;
  background-repeat: no-repeat;
}

#close:hover {
  background-image: -webkit-image-set(
      url('../../../ui/resources/default_100_percent/close_2_hover.png') 1x,
      url('../../../ui/resources/default_200_percent/close_2_hover.png') 2x);
}

#close:active {
  background-image: -webkit-image-set(
      url('../../../ui/resources/default_100_percent/close_2_pressed.png') 1x,
      url('../../../ui/resources/default_200_percent/close_2_pressed.png') 2x);
}