P Class invalidate the plugin

I don’t know how to solve this issue, basically when i put a standard form like this one:

[text* your-firstname placeholder "Nome"]

[text* your-lastname placeholder "Cognome"]

[text* your-telephone placeholder "Telefono con +39"]

[email* your-email placeholder "Email"]

[acceptance accept-this] Seleziona questa casella per confermare la tua presenza all'evento.

[submit class:btn class:btn-accent class:btn-block "Registrati"]

all work great.

But when i try to change the style of the form and i put this:

<p class="wpcf7-inline-field">[text* your-firstname placeholder class:form-fluid "Nome*"]</p>

<p class="wpcf7-inline-field">[text* your-lastname placeholder class:form-fluid "Cognome*"]</p>

<p class="wpcf7-inline-field">[text* your-telephone placeholder class:form-fluid "Telefono con +39*"] </p>

<p class="wpcf7-inline-field">[email* your-email placeholder class:form-fluid "Email*"] </p>

[acceptance accept-this] Seleziona questa casella per confermare la tua presenza all'evento.

[submit class:btn class:btn-accent class:btn-block "Registrati"]

the plugin stop to work!!!!!

So a webmaster need to choose:
1) use your plugin with a shitty style
2) use another plugin with a great style…

There is something we can do to change this? How can i modify the style without compromise the work of the plugin?

https://wordpress.org/plugins/contact-form-7-getresponse-extension/