Give the format to a contact form from a css file (template)

Hi, I’m trying to change the appearance of one contact form, but I do not know what folder should I install my template design and button image and background image. I have a child theme, and I created the folder /public_html/wp-content/themes/customizr-child/inc/assets/css where I pasted these files (estilos1.css and folder of images), but it did not work. I also tried /public_html/wp-content/themes/customizr-child/inc/admin/css and neither worked. I’m not a programmer, I assume that none of these folders is where I should put the files.
This is the form code

<!-- 1  -->
<!-- 2  -->
<link href="PATH/estilos1.css" media="screen" rel="stylesheet" type="text/css" />
<link href='https://fonts.googleapis.com/css?family=Cabin' rel='stylesheet' type='text/css'>

<div class="contenemail">
<p>Rellene el siguiente formulario para suscribirse</p>
<form enctype="application/x-www-form-urlencoded" action="HERE THE FORM LINK" method="post">

    <dl class="zend_form">
        <dt id="name-label">
            <label for="name" class="required">Nombre</label>
        </dt>
        <dd id="name-element">
            <input type="text" name="name" id="name" value="" class="texto"/>
        </dd>
        <dt id="email-label">
            <label for="email" class="required">Email</label>
        </dt>
        <dd id="email-element">
            <input type="text" name="email" id="email" value="" class="texto"/>
        </dd>
		<dt id="submit-label">?</dt>
		<dd id="submit-element">
			<input type="submit" name="submit" id="submit" value="Suscribir" />
		</dd>
	</dl>
</form>
</div>

<div class="extra"></div>

I replaced “THE FORM LINK HERE” with the corresponding link to my email service provider and the PATH where stayed files /public_html/wp-content/themes/customizr-child/inc/admin/css or /public_html/wp-content/themes/customizr-child/inc/assets/css

I appreciate the help that you give me on where I put these files in order that the style is adopted by the form. Thanks