Thumbnails Customization
Use ./core/config/images.php to register custom fizes for images/thumbnails.
| Param | Type | Description | Required | 
|---|---|---|---|
$width | int | Image width | ✔ | 
$height | int | Image height | ✘ | 
$crop | bool/array | Image crop | ✘ | 
return [
  'My Custom Size' => [ 300, 200, true ],
  'My Other Size'  => [ 500, 500, true ],
];
// load the image normally
the_post_thumbnail('My Custom Size');
More info: add_image_size.