{# templates/emails/signup.html.twig #}
{% apply inline_css %}
    <style>
        {# here, define your CSS styles as usual #}
        h1 {
            color: #333;
        }
    </style>
    <img src="{{ email.image('@images/logo.png') }}" alt="Logo">
    <h1>Welcome {{ email.toName }}!</h1>

    <p>
        You signed up as {{ username }} the following email:
    </p>
    <p><code>{{ email.to[0].address }}</code></p>

    <p>
        <a href="#">Click here to activate your account</a>
        (this link is valid until {{ expiration_date|date('F jS') }})
    </p>
{% endapply %}