functions.php

<?php
add_action( 'wp_enqueue_scripts', 'enqueue_child_theme_styles', PHP_INT_MAX);
function enqueue_child_theme_styles() {
  wp_enqueue_style( 'parent-style', get_template_directory_uri().'/style.css' );
}
?>

how to create child theame in wordpress

create child theme folder 

Step 1: Create a folder and name it anything you like. Ex: optimizer-child
Step 2: Create a file titled style.css
Step 3: Open the style.css and write below information

/*
Theme Name: Optimizer Child
Template: optimizer
*/

Step 4: Create a file titled functions.php and paste below code to import the parent themes style.

<?php
add_action( 'wp_enqueue_scripts', 'enqueue_child_theme_styles', PHP_INT_MAX);
function enqueue_child_theme_styles() {
  wp_enqueue_style( 'parent-style', get_template_directory_uri().'/style.css' );
}
?>


 Step 5: Now Zip the folder and upload it via Appearance -> Themes -> Add New
Step 6: Activate the theme.

style.css

/*
Theme Name: Optimizer Child
Template: optimizer
*/