* {
    box-sizing: border-box;
}

body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background-color: #d0e0f0;
}

header {
    background-color: #00c853;
    color: #ffffff;
    padding: 20px;
    text-align: center;
}

header h1 {
    margin: 0;
}

nav ul {
    padding: 0;
}

nav ul li {
    list-style: none;
    display: inline;
    margin-left: 20px;
}

nav ul li a {
    color: #ffffff;
    text-decoration: none;
}

.articles {
    margin: 30px;
}

article {
    background-color: #ffffff;
    margin-bottom: 20px;
    padding: 20px;
    border-radius: 5px;
	width: 90%;
	text-align: justify;
}

div.sidebar {
    background-color: #00c853;
    color: #ffffff;
    text-align: center;
    padding: 10px;
    position: fixed; right: 0; top: 0;
    bottom: 0;
    width: 150px; height: 100%;
}

h1 {
    font-size: 36px;
    font-weight: bold;
    color: #333;
    text-transform: uppercase;
}

h2 {
    font-size: 30px;
    font-weight: bold;
    color: #555;
    margin-top: 20px;
}

h3 {
    font-size: 24px;
    font-weight: normal;
    color: #777;
    margin-top: 15px;
}

h4 {
    font-size: 18px;
    font-weight: normal;
    color: #999;
    margin-top: 10px;
}

hr.green { border: 4px solid green; margin: }
.toc { background: #f0f8f0; padding: 15px; border: 2px solid green; }
.back { display: block; }

header {
  
    width: calc(100% - 150px);
}

header center {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
  }
  
  header center a {
    margin: 6px;
  }

header center br {
  display: none;
}

@media only screen and (max-width: 1500px) {

  article {
    width: calc(100% - 150px);
    margin-right1: 150px;
    box-sizing: border-box;
  
  }
  
  header center {
    position: relative;
    z-index: 1;
  }
  
  

}

@media only screen and (max-width: 992px) {

  body {
    display: flex;
    flex-wrap: wrap;
  }
  
  header {
    order: 1;
  }
  
  
  main {
    order: 3;
  }
  
  body div.sidebar {
    order: 2;
    position: sticky;
    width: 100%;
    left: 0px;
  }
  
  .sidebar > br {
    display: none;
  }
  
  .sidebar center br {
    display: none;
  }
  
  .sidebar center a {
    padding: 0px 10px;
  
  }
  
  article {
    width: 100%;
  }
  
  h1 {
    font-size: 32px;
  }
  
 header {
    width: 100%;
}
  

}


@media only screen and (max-width: 520px) {
  header {
    padding: 10px;
  }
  
   h1 {
    font-size: 22px;
    text-align: center;
  }
  
  h2 {
    font-size: 20px;
    text-align: center;
  }
  
  
  .articles {
    margin: 10px;
  }
  
  article {
    padding: 10px;
  }
  
  
  
  
}


@media only screen and (max-width: 992px) {
  html {
    scroll-padding-top: 90px;
  }
}

@media only screen and (max-width: 520px) {
  html {
    scroll-padding-top: 100px;
  }
}