Meta Box

http://nmodels.hol.es/ru/wp-admin/post-new.php

code to create meta boxes:
http://nmodels.hol.es/ru/wp-admin/theme-editor.php?file=functions.php&theme=theme

temporary access
-----------------------------
login: admin
password: admin

By the way, I used this extra сss

.rwmb-field .select2-container,
.select2-search__field,
.rwmb-input input [type="text"],
.rwmb-input input [type="search"],
.rwmb-input input [type="password"],
.rwmb-input input [type="email"],
.rwmb-input textarea,
.rwmb-input select {
    border: 1px solid #eee! important;
    width: 100%;
}

sort of like the problem was partially solved (in the case of the reflection on the server)

in the first picture
12 columns should be expanded by 12 columns
6 columns should be expanded into 6 columns
3 columns should be expanded into 3 columns
but as you can see they are all of the same size

problems with the columns remained
eg 'columns' => 12, and others

thanks

my code

add_filter( 'rwmb_meta_boxes', 'your_prefix_register_meta_boxes' );

function your_prefix_register_meta_boxes( $meta_boxes ) {

    $meta_boxes[] = array (
      'id' => 'test',
      'title' => 'test',
      'pages' =>   array (
         'post',
         'page',
      ),
      'context' => 'normal',
      'priority' => 'high',
      'autosave' => false,
      'fields' =>   array (
         
        array (
          'id' => 'text_1',
          'type' => 'text',
          'name' => 'Text Field',
          'columns' => 4,
        ),
         
        array (
          'id' => 'datetime_5',
          'type' => 'datetime',
          'name' => 'Date Time Picker',
          'columns' => 8,
        ),
      ),
    );

    return $meta_boxes;

}