chrome/browser/resources/inline_login/inline_login_app.html

<style>
  :host {
    --dialog-top-border-size: 35px;
    display: flex;
    flex-direction: column;
    height: 100%;
  }

  .signin-frame {
    height: 100%;
    margin: 0;
    padding: 0;
    width: 100%;
  }

  .container {
    align-items: center;
    display: flex;
    flex-grow: 1;
    justify-content: center;
  }

<if expr="chromeos">
  .container {
    margin-top: calc(-1 * var(--dialog-top-border-size));
  }
</if>

  .signin-frame {
    background-color: white;
    overflow: hidden;
  }

  .buttons {
    display: flex;
    padding: 0 32px 32px;
  }

  .action-buttons {
    margin-inline-start: auto;
  }

  paper-spinner-lite {
    --spinner-size: 24px;
    display: none;
    height: var(--spinner-size);
    width: var(--spinner-size);
  }

  paper-spinner-lite[active] {
    display: inline-block;
  }
</style>

<div class="container">
  <webview id="signinFrame" name="signin-frame" class="signin-frame"
      hidden$="[[loading_]]" allowscaling></webview>
  <paper-spinner-lite active="[[loading_]]">
  </paper-spinner-lite>
</div>

<if expr="chromeos">
  <div class="buttons" hidden$="[[loading_]]">
    <cr-button class="back-button"
        aria-label="$i18n{accessibleBackButtonLabel}"
        on-tap="handleGoBack_">
      <iron-icon icon="[[getBackButtonIcon_()]]"></iron-icon>
      $i18n{accessibleBackButtonLabel}
    </cr-button>

    <div class="action-buttons" hidden$="[[!enableGaiaActionButtons_]]">
      <gaia-action-buttons authenticator="[[authExtHost_]]">
      </gaia-action-buttons>
    </div>
  </div>
</if>