Magento 2 - How I can rewrite this file

Question

I want to change the following file: vendor/magento/module-paypal/Model/SmartButtonConfig.php but if I made the modifications directly in the vendor file when I will upgrade my store this modifications will be lost. How I can add this file in the app/code or what is the best way to can modify this file?

Thank you

Public function:

private function getButtonStyles(string $page): array
{
    $styles = $this->defaultStyles[$page];
    if ((boolean)$this->config->getValue("{$page}_page_button_customize")) {
        $styles['layout'] = $this->config->getValue("{$page}_page_button_layout");
        $styles['size'] = $this->config->getValue("{$page}_page_button_size");
        $styles['color'] = $this->config->getValue("{$page}_page_button_color");
        $styles['shape'] = $this->config->getValue("{$page}_page_button_shape");
        $styles['label'] = $this->config->getValue("{$page}_page_button_label");
        $styles['height'] = 55;
        $styles['tagline'] = false;
        $styles['fundingicons'] = false;
        $styles = $this->updateStyles($styles, $page);
    }
    return $styles;
}

I want to add only this:

$styles['height'] = 55;
$styles['tagline'] = false;
$styles['fundingicons'] = false;

in the private function getButtonStyles

Answer 1

1. create di.xml file on following location

app\code\Vendor\Extension\etc\frontend\di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="\Magento\Paypal\Model\SmartButtonConfig" type="Vendor\Extension\Model\SmartButtonConfig" />
</config>

2. create SmartButtonConfig.php on following location

app\code\Vendor\Extension\Model\SmartButtonConfig.php

namespace Vendor\Extension\Model;

class SmartButtonConfig extends \Magento\Paypal\Model\SmartButtonConfig
{
   //do the code
}