im trying to stop the scroll in my fixed aside at certain point (before the footer) but im not getting it. I take a look here and other forums but only found jquery solutions and i dont want to use jquery. Here is my html:

<aside>
    <section id="openFormSection">
        <span><mark>Click aquí para abrir el formulario!</mark></span>
        <button id="formMobilIcon">
            CONTACTANOS! <i class="fab fa-wpforms"></i>
        </button>
    </section>
    <form name="contact" method="POST" netlify data-netlify-recaptcha="true">
        <div id="form-container">
            <fieldset id="contact">
                <legend>Formulario de contacto</legend>
                <i class="far fa-times-circle"></i>
                <label for="name">Nombre</label> <input name='name' type='text' id="nombre-input" placeholder="Nombre"> <br>
                <label>¿Cómo te contactamos?</label>
                <label class="cboxes" for="checkboxs"><input type="checkbox" name="checkboxs" id="cboxTelefono" value="Telefono"> Telefono</label>
                <label class="cboxes" for="checkboxs"><input type="checkbox" name="checkboxs" id="cboxEmail" value="Email"> Correo electronico</label>
                <label for="telefono">Telefono</label>
                <input type="text" name="telefono" id="telefono" placeholder="Telefono" disabled> <br>
                <label for="email">Correo electrónico</label>
                <input type="email" name="email" id="email" placeholder="Correo electrónico" disabled> <br>
                <textarea name="textarea" id="textarea" rows="5" cols="15" >Detalla brevemente tu consulta y nos comunicaremos lo mas pronto posible.</textarea>
                <input type="hidden" name="subject" value="formulario contacto urutina-pinturas">
                <div id="captcha" data-netlify-recaptcha="true"></div>
                <button id="sendBtnForm">ENVIAR</button>
                
            </fieldset>
        </div>
    </form>
</aside>

the footer container is sibling of aside.