* {
  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;
}

.top-wrapper p {
  opacity: 0.7;
  font-size: 16px;
  margin-bottom: 40px;
}

.btn-wrapper {
  text-align: center;
}

.btn-wrapper p {
  margin-bottom: 20px;
}

.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: rgb(230, 15, 15);
  font-size: 25px;
  line-height: 25px;
  padding: 15px 15px;
  border-radius: 50%;
  font-weight: bold;
  transition: 0.5s;
}

.header-left a:hover {
  background-color: rgb(196, 72, 111, 0.3);
}

.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(196, 72, 111, 0.3);
}

.lesson-wrapper {
  height: 700px;
  padding-bottom: 80px;
  padding-left: 5%;
  padding-right: -5%;
  background-color: #f8f2f2;
  text-align: center;
}

.heading {
  padding-top: 30px;
  padding-bottom: 50px;
  color: #5f5d60;
}

.heading h1 {
  font-size: 30px;
}

.lesson {
  float: left;
  width: 50%;
}

.lesson-icon {
  position: relative;
}

.lesson-icon p {
  position: absolute;
  top: 37%;
  width: 100%;
  color: white;
}

.text-contents {
  width: 50%;
  display: inline-block;
  margin-top: 15px;
  font-size: 15px;
  color: #b3aeb5;
}

.message-wrapper {
  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: 750px;
  }

  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: 1300px;
  }

  .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;
  }
}