* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  list-style: none;
  text-decoration: none;
}

.sidebar {
  position: fixed;
  /* left: 0; */
  left: -250px; /* checkboxを実装するとき */
  background: #008080;
  width: 250px;
  height: 100%;
  transition: all 0.5s;
  z-index: 100;
}

.sidebar header {
  font-size: 22px;
  color: #fff;
  text-align: center;
  line-height: 70px;
  background: #127d72;
  user-select: none;
}

.sidebar ul a {
  display: block;
  height: 10%;
  width: 100%;
  line-height: 65px;
  font-size: 20px;
  color: #fff;
  padding-left: 40px;
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  border-bottom: 1px solid #d9e3ff;
  transition: 0.4s;
}

.sidebar ul a i {
  margin-right: 16px;
}

#check {
  display: none;
}

label #btn,
label #cancel {
  position: absolute;
  cursor: pointer;
  background: #127d72;
  border-radius: 3px;
}

label #btn {
  left: 40px;
  top: 25px;
  font-size: 25px;
  color: #fff;
  padding: 6px 12px;
  transition: all 0.5s;
}

label #cancel {
  z-index: 10;
  /* left: 195px; 見やすいように最初はこれ*/
  left: -195px;
  top: 17px;
  font-size: 30px;
  color: #fff;
  padding: 4px 9px;
  transition: all 0.5s;
  z-index: 101;
}

#check:checked ~ .sidebar {
  left: 0;
}

#check:checked ~ label #btn {
  left: 250px;
  opacity: 0;
  pointer-events: none;
}

#check:checked ~ label #cancel {
  left: 195px;
}

#check:checked ~ section {
  margin-left: 250px;
}

section {
  height: 100vh;
  background: url(背景画像);
  background-size: cover;
  background-position: center;
  transition: all 0.5s;
}