Source

File: wp-includes/class-wp-customize-panel.php

protected function render_template() {
		?>
		<li id="accordion-panel-{{ data.id }}" class="accordion-section control-section control-panel control-panel-{{ data.type }}">
			<h3 class="accordion-section-title" tabindex="0">
				{{ data.title }}
				<span class="screen-reader-text"><?php _e( 'Press return or enter to open this panel' ); ?></span>
			</h3>
			<ul class="accordion-sub-container control-panel-content"></ul>
		</li>
		<?php
	}