SELECT 
  * 
FROM 
  cscart_bm_containers as c 
  LEFT JOIN cscart_bm_grids as g ON g.container_id = c.container_id 
WHERE 
  1 
  AND g.container_id IN (81, 82, 83, 84) 
ORDER BY 
  g.order, 
  g.parent_id, 
  g.grid_id ASC

Query time 0.00038

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.059631483,
    "nested_loop": [
      {
        "read_sorted_file": {
          "filesort": {
            "sort_key": "g.`order`, g.parent_id, g.grid_id",
            "table": {
              "table_name": "g",
              "access_type": "range",
              "possible_keys": ["container_id"],
              "key": "container_id",
              "key_length": "3",
              "used_key_parts": ["container_id"],
              "loops": 1,
              "rows": 21,
              "cost": 0.02659864,
              "filtered": 100,
              "index_condition": "g.container_id in (81,82,83,84)"
            }
          }
        }
      },
      {
        "table": {
          "table_name": "c",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["container_id"],
          "ref": ["u985510652_ecartify.g.container_id"],
          "loops": 21,
          "rows": 1,
          "cost": 0.01960244,
          "filtered": 100
        }
      }
    ]
  }
}