:root {
  --header-bg:#F1F1F1;
  --nav-bg:#F2F2F2;
  --article-bg:#EDEDEF;
  --border-color:#E0E0E0;
  --sidebar-text-color:#6F7A79;
  --article-text-color:#625F5F;
  --article-heading-color:#929292;
  --nav-link-color:#5f758c;
  --darker-border-color:#C6C6C6;
}
html, body {
  padding:0;
  margin:0;
}
body {
  font-size:12px;
}
body a {
  color:var(--nav-link-color);
}

header, nav {
  max-width:100%;
}
aside {
  width:250px;
  margin-top:30px;
}
.flex {
  display:flex;
  max-width:900px;
}
nav {
  height:auto;
  margin-bottom:10px;
  background-color:var(--nav-bg);
}
header {
  max-height:200px;
  height:200px;
  background-color:var(--header-bg);
  background-image:url('https://learn.sadgrl.online/wp-content/uploads/2022/02/skyline-banner.png');
  background-repeat:repeat-y;
  background-size:600px;
  background-position:fixed;
}
main {
  width:100%;
  margin-left:20px;
  margin-right:20px;
}
section {
  margin-bottom:10px;
  color:var(--sidebar-text-color);
}
article { 
  border:1px solid var(--darker-border-color);
  margin-bottom:15px;
  background-color:var(--article-bg);
  color:var(--article-text-color);
  padding:10px;
}
.subtitle {
  border:1px solid var(--darker-border-color);
  background-color:var(--nav-bg);
}
.links {
  list-style-type:none;
  padding-left:0;
}
.links li {
  background-color:var(--nav-bg);
  border:1px solid var(--border-color);
  margin-bottom:3px;
}
.links li a {
  text-decoration:none;
  color:inherit;
}
.nav {
  margin-top:10px;
  margin-left:100px;
}
.nav li {
  display:inline-block;
  padding-left:30px;
}
.nav li a {
  text-decoration:none;
  text-transform:uppercase;
  color:var(--nav-link-color);
}
.left-sidebar {
  margin-left:50px;
}
.subtitle {
  color:var(--article-text-color);
  font-weight:bold;
  letter-spacing:1px;
}
article .subtitle {
  text-transform:uppercase;
  font-size:16px;
  color:var(--article-heading-color);
  margin-top:10px;
  margin-left:5px;
  margin-right:5px;
  margin-bottom:10px;
  
}
nav {
  border:2px solid var(--darker-border-color);
  border-left:none;
  border-right:none;
}
footer {
  max-width:800px;
  text-align:center;
  color:var(--sidebar-text-color);
}
footer a{
  color:var(--navbar-link-color);
}
@media only screen and (max-width: 800px) {
  .flex {
    flex-wrap:wrap;
  }
  aside {
    display:flex;
    width:100%;
    margin-left:20px;
    margin-right:20px;
  }
  aside > section {
    margin-right:10px;
  }
  .nav {
    margin-left:0 !important;
    margin-right:50px;
  }
  .nav li {
    padding-bottom:5px;
  }
}