<div class="row">
   <div class="col-lg-12">
      <div class="form-group text_box">
         [email* email-520 placeholder "Your Email"]
      </div>
   </div>
   <div class="col-lg-12">
      <div class="form-group text_box">
         [text* text-78 placeholder "Your Name"]
      </div>
   </div>
   <div class="col-lg-12">
      <div class="form-group text_box">
         [textarea textarea-204 placeholder "Enter Your Message . . ."]
      </div>
   </div>
   <div class="col-lg-12">
      [submit class:btn_three "Send Message"]
   </div>
</div>

Note: Add the html_class="contact_form_box" attribute along with the form shortcode to see the output as shown in the demo.