Use the Child-theme:
- Add this CSS code to the file functions.php:
if ( !function_exists( 'custom_single_product_sku' ) ) {
    function custom_single_product_sku()
    {
        global $product;
        if ( wc_product_sku_enabled() && ( $product->get_sku() || $product->is_type( 'variable' ) ) ) : ?>
            <span class="sku_wrapper">
				<?php esc_html_e( 'SKU:', 'woocommerce' ); ?> <span class="sku"><?php echo ( $sku = $product->get_sku() ) ? $sku : esc_html__( 'N/A', 'woocommerce' ); ?></span>
			</span>
        <?php endif;
    }
}
add_action( 'woocommerce_single_product_summary', 'custom_single_product_sku', 5 );

- And add this css code to be the same with the above category:
.sku_wrapper{
font-size: 13px;
line-height: 19px;
}