MD History: Address design nits

chrome/browser/resources/md_history/history_toolbar.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-icons/hardware-icons.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-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-tabs/paper-tab.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-tabs/paper-tabs.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_toolbar/cr_toolbar.html">
 <link rel="import" href="chrome://history/icons.html">
@@ skipping 25 matching lines @@
       #toolbar-container {
         height: var(--toolbar-height);
       }
 
       #overlay-buttons {
         margin: 0 auto;
         max-width: var(--card-max-width);
         padding: 0 var(--card-padding-side);
       }
 
+      paper-button {
+        font-weight: 500;
+      }
+
       #number-selected {
         @apply(--layout-flex);
       }
 
       #cancel-icon-button {
         -webkit-margin-end: 24px;
         -webkit-margin-start: 2px;
         height: 36px;
         min-width: 36px;
         width: 36px;
@@ skipping 93 matching lines @@
               class="rtl-reversible"></paper-icon-button>
           <paper-icon-button icon="cr:chevron-right"
               alt="$i18n{rangeNext}" title="$i18n{rangeNext}"
               class="rtl-reversible"></paper-icon-button>
         </div>
       </div>
     </template>
   </template>
   <script src="chrome://history/history_toolbar.js"></script>
 </dom-module>