[MD History] Use proper shadows for cards.

chrome/browser/resources/md_history/history_item.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-checkbox/paper-checkbox.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="chrome://resources/html/icon.html">
 <link rel="import" href="chrome://resources/html/util.html">
 <link rel="import" href="chrome://history/browser_service.html">
 <link rel="import" href="chrome://history/constants.html">
 <link rel="import" href="chrome://history/searched_label.html">
 <link rel="import" href="chrome://history/shared_style.html">
 
 <dom-module id="history-item">
   <template>
     <style include="shared-style">
       :host {
         display: block;
       }
 
       :host(:not([embedded])) #main-container {
-        background: #fff;
-        border-color: var(--card-border-color);
-        border-style: solid;
-        border-width: 0 1px;
+        position: relative;
       }
 
       :host(:not([embedded])) #sizing-container {
         @apply(--card-sizing);
       }
 
       :host([is-first-item]) #main-container {
         margin-top: var(--first-card-padding-top);
       }
 
       :host([is-card-start]) #main-container {
         border-radius: 2px 2px 0 0;
-        border-top-width: 1px;
       }
 
       :host([is-card-end]) #main-container {
-        border-bottom-width: 2px;
         border-radius: 0 0 2px 2px;
         margin-bottom: var(--card-padding-between);
       }
 
       :host([is-card-start][is-card-end]) #main-container {
         border-radius: 2px;
       }
 
       #date-accessed {
         display: none;
@@ skipping 75 matching lines @@
 
       :host([starred]) #bookmark-star {
         visibility: visible;
       }
 
       #time-gap-separator {
         -webkit-border-start: 1px solid #888;
         -webkit-margin-start: 77px;
         height: 15px;
       }
+
+      #background {
+        background: #fff;
+        bottom: -1px;  /* Prevents shadow artifacts when zoomed */
+        left: 0;
+        position: absolute;
+        right: 0;
+        top: 0;
+        z-index: -1;
+      }
+
+      :host([is-card-end]) #background {
+        bottom: 0;
+      }
     </style>
 
     <div id="sizing-container">
       <div id="main-container">
+        <div id="background"></div>
         <div id="date-accessed" class="card-title">
           [[cardTitle_(numberOfItems, item.dateRelativeDay, searchTerm)]]
         </div>
         <div id="item-container">
           <paper-checkbox id="checkbox" on-tap="onCheckboxSelected_"
               checked="{{selected}}" disabled="[[selectionNotAllowed_()]]">
           </paper-checkbox>
           <span id="time-accessed">[[item.readableTimestamp]]</span>
           <div class="website-icon" id="icon"></div>
           <div id="title-and-domain">
@@ skipping 13 matching lines @@
           </button>
         </div>
         <template is="dom-if" if="[[hasTimeGap]]">
           <div id="time-gap-separator"></div>
         </template>
       </div>
     </div>
   </template>
   <script src="chrome://history/history_item.js"></script>
 </dom-module>