.header {
  position: relative;
  padding: 10px;
}

.hamburger {
position: absolute;
  top: 20px;
  left:20px;
  z-index: 100;
  width: 48px;
  height: 48px;
  border: none;
  background: #eeeeee;
  cursor: pointer;
}

.hamburger__line {
  position: absolute;
  left: 11px;
  width: 26px;
  height: 2px;
  background-color: #333;
  transition: all .4s;
}

.hamburger__line:nth-of-type(1) {
  top: 14px;
}
.hamburger__line:nth-of-type(2) {
  top: 23px;
}
.hamburger__line:nth-of-type(3) {
  top: 32px;
}

/* メニューオープン時 */
.hamburger.active .hamburger__line:nth-of-type(1) {
  transform: translateY(9px) rotate(-45deg);
}
.hamburger.active .hamburger__line:nth-of-type(2) {
  opacity: 0;
}
.hamburger.active .hamburger__line:nth-of-type(3) {
  transform: translateY(-9px) rotate(45deg);
}

.nav {
  position: fixed;
  top: 0;
  left: 0;
  width: 300px;
  height: 100vh;
  background-color: #fff;
  box-shadow: 2px 0 4px rgba(0,0,0,.1);
  transform: translateX(-100%);
  transition: transform .4s;
  z-index: 90;
}

.nav.active {
  transform: translateX(0);
}

.nav__list {
  margin: 0;
  padding: 20px 0 0;
  list-style: none;
}

.nav__item {
  padding: 0 5px;
}

.nav__link {
  display: block;
  padding: 5px 0;
  color: #333;
  text-decoration: none;
  border-bottom: 1px solid #eee;
}