magento-test/app/code/Magento/Theme/etc/adminhtml/system.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <section id="dev" translate="label" type="text" sortOrder="920" showInDefault="1" showInWebsite="1" showInStore="1">
            <group id="js">
                <field id="move_script_to_bottom" translate="label" type="select" sortOrder="25" showInDefault="1" showInWebsite="0" showInStore="0" canRestore="1">
                    <label>Move JS code to the bottom of the page</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>
            </group>
            <group id="css">
                <field id="use_css_critical_path" translate="label comment" type="select" sortOrder="30" showInDefault="1" showInWebsite="0" showInStore="0" canRestore="1">
                    <label>Use CSS critical path</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                    <comment>
                        <![CDATA[<strong class="colorRed">Warning!</strong> Be sure that you have critical.css file for your theme. Other CSS files will be loaded asynchronously.]]>
                    </comment>
                </field>
            </group>
        </section>
    </system>
</config>