Get inline style for entity field

themekit.php

<?php
function themekit_preprocess_paragraph(&$variables) {
  $paragraph = $variables['paragraph'];
  $bundle = $variables['paragraph']->bundle();

  switch ($bundle) {
    case 'simple_small_cta':
      $variables['image_inline_style'] = themekit_get_entity_image_inline_style($paragraph, 'field_image', 'small_cta');
      break;
    case 'simple_large_cta':
      $variables['image_inline_style'] = themekit_get_entity_image_inline_style($paragraph, 'field_image', 'large_cta');
  }
}

function themekit_get_entity_image_inline_style($entity, $field_name, $image_style) {
  $rendered_style = '';

  if (!$entity->$field_name->isEmpty()) {
    $file_entity = $entity->get($field_name)->entity->get('field_image')->entity;

    if ($url = themekit_get_image_style_url($file_entity, $image_style)) {
      $rendered_style = 'style="background-image: url(' . $url . ');"';
    }
  }

  return $rendered_style;
}

function themekit_get_image_style_url(File $file, $image_style) {
  $uri = $file->getFileUri();
  $url = ImageStyle::load($image_style)->buildUrl($uri);
  return $url;
}