* {
    box-sizing: border-box;
  }
  
  body {
    margin: 0;
    font-family: "Hiragino Kaku Gothic ProN";
  }
  
  a {
    text-decoration: none;
  }
  
  .container {
    width: 100%;
    padding: 0 15px;
    margin: 0 auto;
  }
  
  .top-wrapper {
    padding: 180px 0 100px 0;
    background-image: url(top.png);
    background-size: cover;
    color: white;
    text-align: center;
  }
  
  .top-wrapper h1 {
    opacity: 0.9;
    font-size: 45px;
    letter-spacing: 5px;
  }

  .top-wrapper h2 {
    opacity: 0.85;
    font-size: 25px;
    letter-spacing: 5px;
  }
  
  .top-wrapper p {
    opacity: 0.7;
    font-size: 16px;
    margin-bottom: 40px;
  }
  
  .btn-wrapper {
    text-align: center;
  }
  
  .btn-wrapper p {
    margin-bottom: 20px;
  }
  
  .signup {
    background-color: #239b76;
  }
  
  .facebook {
    background-color: #3b5998;
    margin-right: 10px;
  }
  
  .twitter {
    background-color: #55acee;
  }
  
  .btn {
    padding: 8px 24px;
    color: white;
    display: inline-block;
    opacity: 0.8;
    border-radius: 4px;
    text-align: center;
  }
  
  .btn:hover {
    opacity: 1;
  }
  
  .fa {
    margin-right: 5px;
  }
  
  header {
    height: 65px;
    width: 100%;
    background-color: rgba(44, 63, 62, 0.9);
    position :fixed;
    top: 0;
    z-index: 10;
  }
  
  .logo {
    width: 124px;
    margin-top: 20px;
  }
  
  .header-left {
    float: left;
  }

  .header-left h2 {
    line-height: 25px;
    padding: 0 25px;
    color: white;
    float: left;
    display: block;
  }

  .header-left a {
  background-color: white;
  color: rgba(44, 63, 62, 0.9);
  line-height: 25px;
  padding: 15px 15px;
  border-radius: 50%;
  font-weight: bold;
  transition: 0.5s;
  }

  .header-left a:hover {
  background-color: rgba(32, 82, 158, 0.3);
  color: white;
  }
  
  .header-right {
    float: right;
    margin-right: -25px;
  }
  
  .header-right a {
    line-height: 65px;
    padding: 0 25px;
    color: white;
    display: block;
    float: left;
    transition: all 0.5s;
  }
  
  .header-right a:hover {
    background-color: rgba(32, 82, 158, 0.3);
  }
  
  .lesson-wrapper {
    height: 970px;
    padding-bottom: 80px;
    padding-left: 5%;
    padding-right: -5%;
    background-color: #ecf1f8;
    text-align: center;
  }
  
  .heading {
    padding-top: 30px;
    padding-bottom: 50px;
    color: #5f5d60;
  }
  
  .heading h1 {
    font-size: 30px;
  }
  
  .lesson {
    float: left;
    width: 50%;
  }
  
  .lesson-icon1 {
    position: relative;
  }
  
  .lesson-icon1 p {
    position: absolute;
    font-size: 20px;
    top: -15%;
    width: 100%;
    color: rgb(36, 36, 36);
  }

  .lesson-icon2 {
    position: relative;
  }
  
  .lesson-icon2 p {
    position: absolute;
    font-size: 20px;
    top: -15%;
    width: 100%;
    color: rgb(36, 36, 36);
  }
  
  .text-contents {
    width: 90%;
    display: inline-block;
    margin-top: 15px;
    font-size: 15px;
    color: #b3aeb5;
  }
  
  .text-contents_st {
    width: 75%;
    display: inline-block;
    margin-top: 50px;
    font-size: 18px;
    color: rgb(36, 36, 36);
  }
  .heading h3 {
    font-weight: normal;
  }
  
  .message-wrapper {
    /* margin-top: 100px; */
    border-bottom: 1px solid #eee;
    padding-bottom: 80px;
    text-align: center;
  }
  
  .message {
    padding: 15px 40px;
    background-color: #5dca88;
    cursor: pointer;
    box-shadow: 0px 7px #1a7940;
  }
  
  .message:active {
    position: relative;
    top: 7px;
    box-shadow: none;
  }
  
  footer img {
    width: 125px;
  }
  
  footer p {
    color: #b3aeb5;
    font-size: 12px;
  }
  
  footer {
    padding-top: 30px;
    padding-bottom: 20px;
  }
  
  .menu-icon {
    color: white;
    float: right;
    font-size: 25px;
    padding: 21px 0;
    display: none;
  }
  
  .clear {
    clear: left;
  }

  
  @media all and (max-width: 1000px) {
    .lesson {
      width: 50%;
      margin-bottom: 50px;
    }
  
    .lesson-wrapper {
      height: 1200px;
    }
  
    footer {
      text-align: center;
    }
  }
  
  @media all and (max-width: 750px) {
    .top-wrapper h1 {
      font-size: 32px;
    }
  
    .heading h2 {
      font-size: 20px;
    }
  }
  
  @media all and (max-width: 670px) {
    .header-right {
      display: flex;
      flex-direction: column;
      background-color: rgba(44, 63, 62, 0.95);
      position: absolute;
      top: 65px;
      right: 0;
      width: 60%; /* 例えば60% */
      max-width: 300px;
      text-align: center;
      z-index: 9;
      opacity: 0;
      visibility: hidden;
      transition: opacity 0.3s ease;
    }
  
    .header-right a {
      padding: 15px 0;
      border-top: 1px solid rgba(255, 255, 255, 0.1);
    }  
  
    .menu-icon {
      display: block;
    }
  
    .top-wrapper .btn {
      width: 100%;
    }
  
    .twitter {
      margin-top: 10px;
    }
  
    .top-wrapper {
      text-align: left;
    }
  
    .top-wrapper h1 {
      font-size: 24px;
    }
  
    .top-wrapper p {
      font-size: 14px;
    }
  
    .lesson {
      width: 100%;
    }
  
    .lesson-wrapper {
      height: 1700px;
    }
  
    .message-wrapper .btn {
      width: 100%;
    }
    .menu-icon {
      width: 30px;
      height: 25px;
      position: relative;
      cursor: pointer;
      padding: 20px 0;
    }
    
    .menu-icon span {
      background-color: white;
      height: 3px;
      width: 100%;
      position: absolute;
      left: 0;
      transition: all 0.3s;
      margin: 20px 0;
    }
    
    .menu-icon span:nth-child(1) {
      top: 0;
    }
    
    .menu-icon span:nth-child(2) {
      top: 11px;
    }
    
    .menu-icon span:nth-child(3) {
      top: 22px;
    }   
  
    .header-right.active {
      display: flex;
      flex-direction: column;
      background-color: rgba(44, 63, 62, 0.9);
      position: absolute;
      right: 0;
      top: 65px;
      width: 100%;
      display: flex;
      opacity: 1;
      visibility: visible;
    }
  
    .header-right.active a {
      padding: 15px 0;
      border-top: 1px solid #ccc;
      text-align: center;
    }

    .responsive-img {
      width: 100%
    }

    .lesson-icon1 p {
      position: absolute;
      font-size: 20px;
      top: -20%;
      width: 100%;
      color: rgb(36, 36, 36);
    }

    .lesson-wrapper {
      height: 1900px;
    }
  }