Styling forms

Yes. The following CSS is loaded on the page directly before the form:

<style>
  #x_first_name {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_last_name {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_company {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border-color: #222
  }
  #x_address {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_city {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_state {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  select#x_state,
  select#x_country {
    padding: 0 0 0 6px;
    -webkit-appearance: none;
    -moz-appearance: none;
    -webkit-border-radius: 0;
    border-radius: 0;
    -webkit-box-shadow: none;
    box-shadow: none
  }
  #x_country {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_invoice_num {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_po_num {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_reference_3 {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_user_1 {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_user_2 {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_user_3 {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_email {
    width: 250px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_phone {
    width: 125px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_zip {
    width: 125px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #entered_coupon {
    width: 200px;
    height: 30px;
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  #x_description {
    padding: 0 0 0 6px;
    border: 1px solid #222
  }
  label {
    font-weight: 700;
    display: block
  }
  #x_amount {
    width: 100px;
    height: 30px;
    padding: 0 0 0 6px;
    border-color: #222;
    border-width: 1px;
    margin-bottom: 20px;
    margin-right: 10px;
    display: inline
  }
  #x_amount2 {
    width: 100px;
    height: 30px;
    padding: 0 0 0 6px;
    border-color: #222;
    border-width: 1px;
    margin-bottom: 20px;
    display: inline
  }
  #wp_payeezy_payment_form input[type="submit"] {
    width: auto
  }
</style>

You can override any of these by adding !important to the new style rule. For example, if you wanted to make the #x_first_name field 300px wide instead of 250px wide, you could go into Customizer and under Additional CSS, add the following rule:

#x_first_name {
    width: 300px !important;
  }

The would result in the First Name field being 300px wide.