chrome/browser/resources/signin/signin_shared_css.html

<!-- Common styles for signin-related tab modal dialogs. -->
<dom-module id="signin-dialog-shared">
  <template>
    <style>
      a {
        color: var(--google-blue-700);
        text-decoration: none;
      }

      body {
        margin: 0;
        padding: 0;
      }

      .container {
        background-color: white;
        color: #333;
        width: 448px;
      }

      .top-title-bar {
        align-items: center;
        border-bottom: 1px solid var(--paper-grey-300);
        display: flex;
        font-size: 16px;
        height: 52px;
        padding: 0 24px;
      }

      .action-container {
        display: flex;
        justify-content: flex-end;
        padding: 16px;
      }

<if expr="is_macosx or is_linux">
      .action-container {
        flex-flow: row-reverse;
        justify-content: flex-start;
      }
</if>

    </style>
  </template>
</dom-module>