My code is causing the responsivness in my theme to not work

I added this code

<form action="http://12.178.102.99/formpost.php" method="POST">
<fieldset>
<p class="form_element" ><input class="text_input" name="name" placeholder="Name*" required></p>
<p class="form_element" ><input class="text_input" name="email" placeholder="Email*" required></p>
<p class="form_element" ><input class="text_input" name="phone" placeholder="Phone Number*" required></p>
<input class="button" type="submit" /></fieldset> </div></section></div>
</form>

when I add it it in a code block it breaks the other elements of my theme and make things unresponsive. Any clue why?