Conditionally add IE style sheets in WP

functions.php

<?php

add_action( 'wp_print_styles', 'child_add_ie7_style_sheet', 200 );
/**
 * Enqueue an IE-specific style sheet (for all browsers).
 *
 * @author Gary Jones
 * @link https://garyjones.io/ie-conditional-style-sheets-wordpress
 */
function child_add_ie7_style_sheet() {
	wp_enqueue_style( 'ie7', get_stylesheet_directory_uri() . '/style-ie7.css', [], '1.0' );
}

add_filter( 'style_loader_tag', 'child_make_ie7_style_sheet_conditional', 10, 2 );
/**
 * Add conditional comments around IE7-specific style sheet link.
 *
 * @author Gary Jones & Michael Fields (@_mfields)
 * @link https://garyjones.io/ie-conditional-style-sheets-wordpress
 *
 * @param string $tag    Existing style sheet tag.
 * @param string $handle Name of the enqueued style sheet.
 * @return string Amended markup.
 */
function child_make_ie7_style_sheet_conditional( $tag, $handle ) {
	if ( 'ie7' == $handle ) {
		$tag = '<!--[if lte IE 7]>' . "\n" . $tag . '<![endif]-->' . "\n";
	}
	
	return $tag;
}

Change:

add_action( 'wp_print_styles', 'child_add_ie7_style_sheet', 200 );

To:

add_action( 'wp_enqueue_scripts', 'child_add_ie7_style_sheet', 200 );

Please see: http://core.trac.wordpress.org/ticket/19510 :)