div.container {
  display: flex;
  flex-direction: column;
  align-items: center;
}

div.container h1 {
  display: inline-block;
  width: 100%;
}

div.container form {
  width: 100%;
}

.mailform {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: 100%;
}

.mailform dl {
  display: flex;
  flex-direction: column;
  width: 100%;
}

.mailform dl dt {
  width: 100%;
  font-weight: bold;
}

.mailform dl dd {
  width: 100%;
}

.mailform dl {
  padding: 12px;
  margin-bottom: 1.5em;
  display: flex;
  flex-direction: column;
}

.mailform dt {
  width: 100%;
  display: table-cell;
  vertical-align: middle;
}

@media screen and (max-width: 480px) {
  .mailform dt {
    width: 100%;
  }
}

.mailform dd {
  width: 100%;
  display: table-cell;
  vertical-align: middle;
}

@media screen and (max-width: 480px) {
  .mailform dd {
    width: 100%;
  }
}

.mailform dd input[type="text"],
.mailform dd select,
dd textarea {
  width: calc(100% - 24px);
  font-family: inherit;
  padding: 7px 12px;
  font-size: 16px;
  background: transparent;
  border: none;
  border-radius: 0;
  box-shadow: none;
  border-bottom: solid thin gray;
  color: black;
}

.mailform dd input[type="radio"],
.mailform dd input[type="checkbox"] {
  box-shadow: none;
  border: solid thin gray;
  transform: translate(0, -0.25em);
}

.mailform dd input[type="checkbox"] {
  position: relative;
  margin: 0;
  padding: 0;
  background: none;
  border: none;
  border-radius: 0;
  outline: none;
  appearance: none;
  border: solid thin gray;
  width: 1em;
  height: 1em;
  border-radius: 0.5em;
  transform: translate(0, -0.125em);
}

.mailform dd input[type="checkbox"]::after {
  content: "";
  display: inline-block; 
  position: absolute;
  opacity: 0; /*チェック前は非表示*/
  width: 0.6em; /*チェックの横幅*/
  height: 0.6em; /*チェックの高さ*/
  inset: 0; /*チェック時の位置調整*/
  padding: 0;
  margin: auto;
  border-radius: 0.3em;
  background: gray;
}

.mailform dd input[type="checkbox"]:checked {
  border: solid thin dodgerblue;
}

.mailform dd input[type="checkbox"]:checked::after {
  opacity: 1; /*チェック後表示*/
  background: dodgerblue;
}

.mailform dd .nest {
  padding-left: 45px;
  margin: 10px 0;
}

.mailform dd textarea {
  width: 350px;
  height: 120px;
  box-sizing: border-box;
  resize: vertical;
}

.confirmation_btn {
  font-family: inherit;
  padding: 10px 30px;
  font-size: 16px;
  background: none;
  border-radius: 8px;
  border: none;
  background: #5d3fff;
  color: #fff;
  cursor: pointer;
}

.confirmation_btn:hover {
  opacity: .8;
}

dl.ID_UpLoad dd {
  padding: 0.5em 0 0 0;
}

dl.ID_UpLoad dd label {
  display: inline-block;
  text-align: center;
  cursor: pointer;
  font-size: 16px;
  padding: 0.5em 0;
  width: 100%;
}

dl.ID_UpLoad dd input[type="file"] {
  background: transparent;
  cursor: pointer;
  width: 100%;
  font-size: 16px;
  border-radius: 0;
  border: none;
}

dl.ID_UpLoad dd input[type="file"]::file-selector-button,
dl.ID_UpLoad dd input[type="file"]::-webkit-file-upload-button {
  background: transparent;
  cursor: pointer;
  border: solid medium #00A6D8;
  color: #00A6D8;
  padding: 0.5em 1em;
  margin-right: 1em;
}

input[type="submit"] {
  background: transparent;
  border: none;
  border-radius: 0;
  width: 50%;
  padding: 0.5em 0;
  background: #E58100;
  color: white;
  font-weight: normal;
  font-size: 16px;
}

strong {
  display: inline-block;
  width: fit-content;
  height: fit-content;
  padding: 2px 8px;
  background: red;
  border-radius: 4px;
  color: white;
  font-weight: normal;
  font-size: 16px;
  transform: scale(75%);
}

@media screen and (max-width: 480px) {
  
  div.container {
    width: calc(100% - 60px);
  }

}