
<style>
* {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 0;
  font-family: Arial, sans-serif;
}

header {
  background-color: #f1f1f1;
  padding: 10px;
  text-align: center;
}

/* Top navigation bar */
ul.topnav {
  display:  flex;
  list-style-type: none;
  margin: 0;
  padding: 0;
  background-color: #333333;
}

ul.topnav li a {
  display: block;
  color: #f1f1f1;
  padding: 14px 16px;
  text-decoration: none;
}

ul.topnav li a:hover {
  background-color: #dddddd;
  color: black;
}

/* Flexbox 2-column layout */
.flex-container {
  display:  flex;
  flex-direction: row;
  padding: 10px;
}

/*Make both columns the same width*/
.flex-container > div {
  background-color: #f1f1f1;
  flex: 1;               /* makes both columns equal width */
  margin: 10px;
  padding: 10px;
  text-align: center;
  font-size: 20px;
}

/* Sidebar and main content styling */
.flex-container > div {
  margin: 10px;
  padding: 10px;
  background-color: #f9f9f9;
}

/* Sidebar width */
.sidebar {
  flex: 30%;
  background-color: #d3d3d3;
}

/* Main content width */
.main {
  flex: 70%;
  background-color: #ffffff;
}

/* Footer styling */
footer {
  background-color: #ADD8E6;
  padding: 8px;
  text-align: center;
}

/* Responsive for smaller screens */
@media screen and (max-width:600px) {
  .flex-container {
    flex-direction: column;
  }
}
</style>