How to simulate a Click() for a button using JavaScript in CefSharp.OffScreen

I try to make a CefSharp.OffScreen application to simulate a login. But when the website has pop-up screen that opens the log in screen, I cannot click on that login button.

For example, for the html code below it is a sign in button that opens a pop up screen to enter email and password.

<spark-button size="medium" full variant="secondary" data-linkname="header-sign-in" data-component="sign-in-start" data-click-intent-id="menu-header-sign-in-link-click" data-activity-rule-type="page-over-page"> 
<button part="base" class="button" type="button" aria-disabled="false" tabindex="0">
        <span part="prefix" class="button__prefix">
          <slot name="prefix"></slot>
        </span>
        <span part="label" class="button__label">
          <slot></slot>
        </span>
        <span part="suffix" class="button__suffix">
          <slot name="suffix"></slot>
        </span>
     </button>
"Sign in" 
</spark-button>

I can simulate click on other buttons with document.getElementsByClassName('nav-user-menu-button')[0].click(); javascript code

But, I cannot do it for that sign in button.

I try document.getElementsByClassName("spark-button[data-link-name='header-sign-in']")[0].click(); but it gives error as it is does not include click function.

How can I solve the error?