Override user login form template
if you overrided correctly element will contain all items in form--user-login.html.twig,
&lt;div class=&quot;login-form login-form__wrapper&quot;&gt;
    &lt;form{{ attributes }}&gt;
        &lt;div class=&quot;login-form__top&quot;&gt;
            &lt;h3&gt;hello world&lt;/h3&gt;
            &lt;div id=&quot;error_messages&quot;&gt;&lt;/div&gt;
            {{ element.messages }}
            {{ element.name }} {# username element #}
            {{ element.pass }} {# password element #}
            &lt;div class=&quot;login-form__help_actions&quot;&gt;
                &lt;input id=&quot;show_password&quot; class=&quot;show_password&quot; type=&quot;checkbox&quot; /&gt;
                &lt;label class=&quot;password-toggle&quot; for=&quot;show_password&quot;&gt;Show password&lt;/label&gt;
                &lt;a href=&quot;/user/password&quot; class=&quot;forgot-password&quot;&gt;Forgot Password?&lt;/a&gt;
            &lt;/div&gt;
            {{ element.form_build_id }} {# required #}
            {{ element.form_id }} {# required #}
            &lt;div class=&quot;login-form__submit&quot;&gt;
                {{ element.actions.submit }}
            &lt;/div&gt;
        &lt;/div&gt;
    &lt;/form&gt;
&lt;/div&gt;

if the template is not valid, you should try to add it.
function Yourtheme_theme_suggestions_alter(array &amp;$suggestions, array $variables, $hook) {

  if ($hook == 'form' &amp; !empty($variables['element']['#id'])) {
    $suggestions[] = 'form__' . str_replace('-', '_', $variables['element']['#id']);
  }
}

then create form--user-login-form.html.twig in your theme.
do not forget to clear the cache.