* {
  box-sizing: border-box;
}

/* BODY */
body {
  font-family: Arial;
  margin: 0;
}

/* HEADER */
.header {
  background-color: white;
  padding: 10px;
  text-align: center;
}

/* NAVIGATION BAR */
ul {
  list-style-type: none;
  display:table;
  margin:0 auto;
  padding: 0;
  text-align: center;
  overflow: hidden;
  background-color: #3399FF;
}

li {
  float: left;
  border-right:1px solid white;
  display:inline;
}

li a, .dropbtn {
  display: inline-block;
  color: #f2f2f2;
  text-align: center;
  display:inline-block;
  padding: 14px 16px;
  text-decoration: none;
}

li a:hover, .dropdown:hover .dropbtn {
  background-color: #FFFF00;
  color: blue;
}

li.dropdown {
  display: inline-block;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #3399FF;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  z-index: 1;
}

.dropdown-content a {
  color: white;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
  text-align: left;
}

.dropdown-content a:hover {
  background-color: #FFFF00;
  color: blue;
}

.dropdown:hover .dropdown-content {
  display: block;
}

/* COLUMNS & FOOTER */
#wrapper {
	width: 100%;
	margin: 0 auto;
}

#column-left {
	width: 15%;
	margin: 1%;
	float: left;
    background: white;
}
 
#column-center {
	width: 64%;
	margin: 1%;
	float: left;
}
 
#column-right {
	width: 15%;
	margin: 1%;
	float: left;
	background: white;
}
 
#footer {
  background-color: #3399FF;
  text-align: center;
  color: #f2f2f2;
  max-width: 700px;
  padding: 10px;
  clear: both;
  margin:0 auto;
}

/* IMAGES */
img {
  max-width: 100%;
  height: auto;
}

/* HYPERLINKS */
a:hover {
  color: red;
}

/* selected link */
a:active {
  color: green;
}

/* FLEXBOXES */
.flex-container1 {
  display: flex;
  flex-direction: column;
  align-items: center;
  margin: 25px 0 0 0;
}

.flex-container1 > .TopYellow {
  border: 2px solid blue;
  border-radius: 12px;
  padding: 10px;
  max-width: 600px;
  margin:0 auto; 
  text-align: justify;
  color: blue;
  background-color: #FFFF99;
}

.flex-container2 {
  display: flex;
  flex-direction: column;
  align-items: center;
  margin:0 auto;
}

.flex-container2 > div {
  max-width: 600px;
  margin:0 auto; 
  text-align: justify;
  color: blue;
}

/* RESPONSIVE LAYOUT */
@media screen and (max-width: 600px) {
  #column-left {
    display: none;
  }
  
@media screen and (max-width: 600px) {
  #column-right {
    display: none;
  }

@media screen and (max-width: 600px) {
  #column-center, #column-left, #column-right {
    width: 100%;
  }
  
@media screen and (max-width: 600px) {
  li {
  width: 100%;
  }
}