header {
  display: flex;
  width: 100%;
  height: 100px;
  background-color: #FFFFFF;
  align-items: center;
  position: fixed;/*固定する*/
}
 
p {
  padding: 0px 0px;
  height: 0px;
}
 
.title {
  margin-right: auto;
}
 
.menu-item {
  list-style: none;
  display: inline-block;
  padding: 0px;
}