Font size should be specified as a percentage.

chrome/browser/resources/settings/settings_page/settings_subpage_search.html

 <link rel="import" href="chrome://resources/cr_elements/cr_search_field/cr_search_field_behavior.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input-container.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 
 <dom-module id="settings-subpage-search">
   <template>
     <style>
       paper-input-container {
         width: var(--paper-input-max-width);
       }
 
       input[type='search']::-webkit-search-cancel-button {
         -webkit-appearance: none;
       }
 
       #prompt,
       #searchInput {
-        font-size: 13px;
+        font-size: inherit;
         line-height: 36px;
       }
 
       #prompt {
         color: var(--google-grey-500);
       }
 
       #searchInput {
         color: var(--paper-grey-800);
       }
@@ skipping 20 matching lines @@
       <input is="iron-input" id="searchInput" type="search"
           aria-labelledby="prompt" incremental>
       </input>
       <paper-icon-button suffix icon="cr:cancel" id="clearSearch"
           on-tap="onTapClear_" title="[[clearLabel]]" hidden$="[[!lastValue_]]">
       </paper-icon-button>
     </paper-input-container>
   </template>
   <script src="settings_subpage_search.js"></script>
 </dom-module>