Using ACF to create a stylesheet

branding-stylesheet.php

<?php  /* Brand Colour */ $colour = get_field( 'colour', 'option' ); ?>
.brand--background{ background-color: <?php echo $colour ?>; }
.brand--colour{ color: <?php echo $colour ?>; }
.brand--border{ border-color: <?php echo $colour ?>; }

functions.php

<?php
/**
 * Generate stylesheet for Branding when ACF options are saved
 */
function generate_options_css() {
  $ss_dir = get_stylesheet_directory();
  ob_start(); // Capture all output into buffer
  require($ss_dir . '/assets/branding-css.php'); // Grab the custom style php file
  $css = ob_get_clean(); // Store output in a variable, then flush the buffer
  file_put_contents($ss_dir . '/assets/css/brand.css', $css, LOCK_EX); // Save it as a css file
  }
add_action( 'acf/save_post', 'generate_options_css' ); //Parse the output and write the CSS file on post save

/**
 * Enqueue stylesheet in wp_head
 */
add_action( 'wp_head', 'branding_styles' );
function branding_styles(){
  wp_enqueue_style( 'branding-css', get_stylesheet_directory_uri() . '/assets/css/brand.css' );
}