Drupal7 customizing theme part.1

Customizing theme is not so hard if you understand the structure of php files in theme folder.
I added the setting for the body width.
First, I added the setting of "body_width" in .info file.
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<xxx.info>
; Settings
settings[body_width] = 75%
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Then, I wrote the code which prompts users to enter the setting values in theme-settings.php.
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<theme-settings.php>
function holiday_form_system_theme_settings_alter(&$form, $form_state) {
$form['theme_settings']['body_width'] = array(
    '#type' => 'textfield',
    '#title' => t('Body width'),
    '#default_value'   => theme_get_setting('body_width'),
    '#size' => 12,
    '#maxlength' => 8,
    '#element_validate' => array('holiday_body_width_validate'),
);
}
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After that, go to "Appearance" menu, click the setting of your theme. you'll see "Body width" setting.

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