.header {
  width: 100%;
  z-index: 3;
}

 .header ul {
  margin: 0;
  padding: 0;
  list-style: none;
  overflow: hidden;
}


/* menu */

.header .menu {
  clear: both;
  max-height: 0;
  transition: max-height .2s ease-out;
}

/* menu icon-hamburger */

.header .menu-hamburger {
  cursor: pointer;
  float: right;
 padding: 10px 0;
  position: relative;
  user-select: none;
} 

.header .menu-hamburger .nav-icon {
  background-color: #189595;
  background-color: rgba(17, 128, 128, .9);
  display: block;
  height: 4px;
  position: relative;
  transition: background .2s ease-out;
  width: 30px;
}

.header .menu-hamburger .nav-icon:before,
.header .menu-hamburger .nav-icon:after {
  /* background: #bbb; */
  background-color: #189595;
  background-color: rgba(17, 128, 128, .9);
  content: '';
  display: block;
  height: 100%;
  position: absolute;
  transition: all .2s ease-out;
  width: 100%;
}

.header .menu-hamburger .nav-icon:before {
  top: 10px;
}

.header .menu-hamburger .nav-icon:after {
  top: -10px;
}


/* menu btn */

.header .menu-btn {
  display: none;
}

.header .menu-btn:checked ~ .menu {
  max-height: 400px;
}

.header .menu-btn:checked ~ .menu-hamburger .nav-icon {
  background: transparent;
}

.header .menu-btn:checked ~ .menu-hamburger .nav-icon:before {
  transform: rotate(-45deg);
  top:0;
}

.header .menu-btn:checked ~ .menu-hamburger .nav-icon:after {
  transform: rotate(45deg);
  top:0;
}


/* 50em = 800px (@ 16px font height ) */
@media only screen and (min-width : 50em) {


.header ul {padding: 1em 0;}

.header .menu {
  clear: none;
  float: right;
  max-height: none;
} 
  .header .menu-hamburger {
    display: none;
  }
}