I'm following this alanstorm tutorial and when I'm trying to load the backend page I've got this error:

Fatal error: Uncaught Error: Class 'Mage_Antonino-banner_Helper_Data' not found

Probably there's some typo or some naming convention error, but I really cannot find it.

My app/code/local/Antonino/Banner/etc/config.xml is

<?xml version="1.0" encoding="UTF-8" ?>
<config>
    <modules>
        <Antonino_Banner>
            <version>1.0.0</version>
        </Antonino_Banner>
    </modules>
    <global>
        <models>
            <banner>
                <class>Antonino_Banner_Model</class>
            </banner>
        </models>
        <helpers>
            <banner>
                <class>Antonino_Banner_Helper</class>
            </banner>
        </helpers>
    </global>
</config>

And my app/code/local/Antonino/Banner/etc/system.xml is

<?xml version="1.0" encoding="UTF-8" ?>
<config>
    <tabs>
        <antonino_banner translate="label" module="antonino-banner">
            <label>Antonino</label>
            <sort_order>350</sort_order>
        </antonino_banner>
    </tabs>
    <sections>
        <antoninobanner translate="label" module="antonino-banner">
            <label>Banner Config Options</label>
            <tab>antonino_banner</tab>
            <frontend_type>text</frontend_type>
            <sort_order>300</sort_order>
            <show_in_default>1</show_in_default>
            <show_in_website>1</show_in_website>
            <show_in_store>1</show_in_store>
            <groups>
                <general translate="label">
                    <label>General</label>
                    <frontend_type>text</frontend_type>
                    <sort_order>5</sort_order>
                    <show_in_default>1</show_in_default>
                    <show_in_website>1</show_in_website>
                    <show_in_store>1</show_in_store>
                    <fields>
                        <choose_category translate="label comment">
                            <label>Choose Category</label>
                            <comment>Select the category to which apply the banner</comment>
                            <frontend_type>select</frontend_type>
                            <source_model>banner/categories</source_model>
                            <show_in_default>1</show_in_default>
                            <show_in_website>1</show_in_website>
                            <show_in_store>1</show_in_store>
                        </choose_category>
                    </fields>
                </general>
                <anothergroup translate="label">
                    <label>Another Group</label>
                    <frontend_type>text</frontend_type>
                    <sort_order>5</sort_order>
                    <show_in_default>1</show_in_default>
                    <show_in_website>1</show_in_website>
                    <show_in_store>1</show_in_store>
                </anothergroup>
            </groups>
        </antoninobanner>
        <antoninobannertwo translate="label" module="antonino-banner">
            <label>Another section</label>
            <tab>antonino_banner</tab>
            <frontend_type>text</frontend_type>
            <sort_order>300</sort_order>
            <show_in_default>1</show_in_default>
            <show_in_website>1</show_in_website>
            <show_in_store>1</show_in_store>
        </antoninobannertwo>
    </sections>
</config>

The error shows when i the method Mage::helper('banner')->__('Hello') in app/code/local/Antonino/Banner/Model/Categories.php which code is

<?php
    
class Antonino_Banner_Model_Categories extends Mage_Core_Helper_Abstract
{
    public function toOptionArray()
    {
        return array(
            array('value'=>1, 'label'=>Mage::helper('banner')->__('Hello')),
            array('value'=>2, 'label'=>Mage::helper('banner')->__('Goodbye')),
            array('value'=>3, 'label'=>Mage::helper('banner')->__('Yes')),
            array('value'=>4, 'label'=>Mage::helper('banner')->__('No')),
        );
    }

}

Someone could pls help me? I really cannot figure out why this is not working. Thanks!