Voxel provides a default email notification template that is used for all email notifications

The template adds default site logo from WP admin ➝ Appearance ➝ Customizer 

It uses the Accent Color from Elementor global settings.

Other details can be configured in general settings

Overriding via child theme

To override this template, you can install Voxel child theme

Copy the following file from main theme to child theme
templates/emails/default-template.php

Then edit the file in the child theme and proceed to apply your changes

Override using hook

You can use the following hook to override the built-in email template: 

voxel/emails/custom-template

For example

add_filter( 'voxel/emails/custom-template', function( $template, $message ) {
    return "
        <h2>My custom HTML template</h2>
        <p>{$message}</p>
    ";
}, 10, 2 );