.header {
  position: fixed;
  top: 0;
  width: 100%;
  height: 50px;
  background-color: darkgrey;
  text-align: center
}
 
.main {
  padding-top: 100px;
  overflow: auto;
  text-align: center
}
 
.footer {
  position: fixed;
  bottom: 0;
  width: 100%;
  height: 50px;
  background-color: darkgrey;
}

ul {
    display: flex;
    justify-content: center;
  }

  li {
    margin: 10px;
    list-style: none;
  }

.list_text {
    padding:  1px;             /* 余白指定 */
    margin-left: 48px ;         /* 要素と要素の間指定 */
    font-size:  12px;           /* 文字サイズ指定 */
}