A function for updating the version in the query string for a theme's default stylesheet.

wp_default_styles_version.php

<?php

/**
 * Updates the v= query string for
 * theme's default stylesheet for
 * browser cache busting etc.
 */

function theme_wp_default_styles_version($styles) {
  // use date  versioning or semantic versioning
  $styles->default_version = "vYYYY-MM-DD";
}

add_action("wp_default_styles", "theme_wp_default_styles_version");

?>