『フォーム』に以下のコードをコピペ

<div class="cf7">
  <dl class="cf7__list">
    <dt><span class="cf7__required">必須</span>お問い合わせ分野</dt>
    <dd class="cf7__select">[select menu first_as_label "選択してください" "メニュー１" "メニュー２" "メニュー３" "メニュー４" "メニュー５" "メニュー６" "メニュー７" "メニュー８" "メニュー９" "メニュー１０"]</dd>
    <dt><span class="cf7__required">必須</span>お問い合わせ分野</dt>
    <dd>[radio your-radio use_label_element default:1 "オプション１" "オプション２" "オプション３"]</dd>
    <dt><span class="cf7__required">必須</span>お問い合わせ分野</dt>
    <dd>[checkbox checkbox use_label_element "チェックボックス１" "チェックボックス２" "チェックボックス３"]</dd>
    <dt><span class="cf7__optional">任意</span>会社名</dt>
    <dd>[text your-company-name placeholder "株式会社●●●●"]</dd>
    <dt><span class="cf7__required">必須</span>お名前</dt>
    <dd>[text* your-name placeholder "山田 花子"]</dd>
    <dt><span class="cf7__optional">任意</span>ふりがな</dt>
    <dd>[text* your-name placeholder "やまだ はなこ"]</dd>
    <dt><span class="cf7__required">必須</span>電話番号</dt>
    <dd>[tel your-tel placeholder "000-0000-0000"]</dd>
    <dt><span class="cf7__required">必須</span>メールアドレス</dt>
    <dd>[email* your-email placeholder "example@example.com"]</dd>
    <dt><span class="cf7__required">必須</span>お問い合わせ内容</dt>
    <dd>[textarea your-message 40x10]</dd>
  </dl>
  <div class="cf7__button">[submit "送信する"]</div>
</div>

.cf7__list {
  display: flex;
  flex-wrap: wrap;
  margin-bottom: 60px;
}

.cf7__list dt:nth-of-type(n + 2),
.cf7__list dd:nth-of-type(n + 2) {
  margin-top: 30px;
}

.cf7__list dt {
  width: 35%;
  padding-top: 15px;
}

.cf7__list dd {
  width: 65%;
}

/* 必須・任意 */
.cf7__required,
.cf7__optional {
  margin-right: 15px;
  padding: 6px 14px;
  color: #fff;
  font-size: 12px;
  vertical-align: 1px;
}

.cf7__required {
  background: #BE1D1D;
}

.cf7__optional {
  background: #878D8E;
}

/* input・textarea */
.cf7__list dd input[type="text"],
.cf7__list dd input[type="tel"],
.cf7__list dd input[type="email"],
.cf7__list dd textarea {
  width: 100%;
  padding: 15px 20px;
  background: #F4F4F4;
}

/* ドロップダウンメニュー */
.cf7__select {
  position: relative;
}

.cf7__select:before {
  position: absolute;
  top: 50%;
  right: 20px;
  z-index: 10;
  transform: translateY(-50%);
  width: 0;
  height: 0;
  border-top: 8px solid #000;
  border-right: 6px solid transparent;
  border-left: 6px solid transparent;
  pointer-events: none;
  content: '';
}

.cf7__select select {
  width: 100%;
  padding: 19px 20px;
  background: #F4F4F4;
  color: #a5a5a5;
  -webkit-appearance: none;
     -moz-appearance: none;
          appearance: none;
}

/* チェックボックス・ラジオボタン */
.cf7__list dd .wpcf7-checkbox,
.cf7__list dd .wpcf7-radio {
  display: block;
  padding: 15px 0 10px;
}

/* 縦並び（チェックボックス・ラジオボタン） */
.cf7__list dd .wpcf7-list-item {
  display: block;
  margin: 0;
}

.cf7__list dd .wpcf7-list-item:nth-child(n + 2) {
  margin-top: 18px;
}

/* マウスカーソル（チェックボックス・ラジオボタン） */
.cf7__list dd .wpcf7-list-item label {
  cursor: pointer;
}

/* チェックボックス・ラジオボタン */
input[type="checkbox"],
input[type="radio"] {
  position: relative;
  width: 18px;
  height: 18px;
  margin-right: 8px;
  border: 1px solid #bcbcbc;
  vertical-align: -3px;
  cursor: pointer;
  -webkit-appearance: none;
     -moz-appearance: none;
          appearance: none;
}

/* チェックボックス */
input[type="checkbox"]:checked {
  border: 1px solid #000;
  background: #000;
}

input[type="checkbox"]:checked:before {
  position: absolute;
  top: 2px;
  left: 5px;
  transform: rotate(50deg);
  width: 6px;
  height: 10px;
  border-right: 2px solid #fff;
  border-bottom: 2px solid #fff;
  content: '';
}

/* ラジオボタン */
input[type="radio"] {
  border-radius: 50%;
}

input[type="radio"]:checked:before {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 9px;
  height: 9px;
  border-radius: 50%;
  background: #000;
  content: '';
}

/* プレースホルダー */
/* Google Chrome / Safari / Mozilla Firefox / Opera */
.cf7__list dd input[type="text"]::placeholder,
.cf7__list dd input[type="tel"]::placeholder,
.cf7__list dd input[type="email"]::placeholder,
.cf7__list dd textarea::placeholder {
  color: #a5a5a5;
}

/* Microsoft Edge */
.cf7__list dd input[type="text"]::-ms-input-placeholder,
.cf7__list dd input[type="tel"]::-ms-input-placeholder,
.cf7__list dd input[type="email"]::-ms-input-placeholder,
.cf7__list dd textarea::-ms-input-placeholder {
  color: #a5a5a5;
}

/* Internet Explorer */
.cf7__list dd input[type="text"]:-ms-input-placeholder,
.cf7__list dd input[type="tel"]:-ms-input-placeholder,
.cf7__list dd input[type="email"]:-ms-input-placeholder,
.cf7__list dd textarea:-ms-input-placeholder {
  color: #a5a5a5;
}

/* 送信ボタン */
.cf7__button {
  padding-left: 72px;
  text-align: center;
}

input[type="submit"] {
  width: 260px;
  height: 60px;
  background: #000;
  color: #fff;
  transition: opacity .6s;
}

input[type="submit"]:hover {
  opacity: .6;
}

/* ajax-loader */
.wpcf7-spinner {
  vertical-align: middle;
}

@media screen and (max-width: 767px) {

  .cf7__list dt {
    width: 100%;
    margin-bottom: 15px;
    padding-top: 0;
  }

  .cf7__list dd {
    width: 100%;
  }

  .cf7__list dd:nth-of-type(n + 2) {
    margin-top: 0;
  }

  .cf7__list dd .wpcf7-checkbox,
  .cf7__list dd .wpcf7-radio {
    padding: 15px 0 0;
  }

  /* 送信ボタン */
  input[type="submit"] {
    width: 180px;
    height: 56px;
  }

}