* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
}

.header {
  text-align: center;
  padding: 30px;
}

.header h1 {
  font-size: 36px;
  letter-spacing: 3px;
}

.header h2 {
  font-size: 24px;
  font-stretch: expanded;
}

.blocktext {
  width: 100%;
  max-width: 860px;
  margin: 0 auto;
  text-align: justify;
  padding-top: 20px;
  padding-left: 40px;
  padding-right: 25px;
  font-size: 1.2em;
}

.footer {
  text-align: center;
  color: white;
  background-color: #333;
  padding: 8px;
  margin-top: 16px;
}

.footer a {
  color: white;
}

.nav {
  overflow: hidden;
  background-color: #333;
}

.nav a {
  float: left;
  color: #f2f2f2;
  text-align: center;
  padding: 14px 26px;
  text-decoration: none;
  font-size: 17px;
}

.nav a:hover {
  background-color: #ddd;
  color: black;
}

.nav a.active {
  background-color: #CCCCCC;
  color: black;
}

.figure {
  position: relative;
  margin: 4px
}

.figure img {
  width: 100%
}

.figcaption {
  box-sizing: border-box;
  width: 100%;
  padding: 10px;
  margin-bottom: 4px;
  position: absolute;
  bottom: 0;
  left: 0;
  background-color: rgba(0, 0, 0, 0.5);
  color: white
  }

.figcaption {
  visibility: none;
  opacity: 0;
  transition: opacity 0.3s
}

.figure:hover .figcaption {
  visibility: visible;
  opacity: 1
}

.thumbs {
  max-width: 860px;
  margin: 0 auto;
  color: white;
}

.thumbs ul {
  margin-top: 0;
  margin-bottom: 0;
}

.thumbs li {
  display: inline;
  list-style-type: none;
}

.thumbs img {
  margin: 2px;
}

.row {
  display: -ms-flexbox; /* IE10 */
  display: flex;
  -ms-flex-wrap: wrap; /* IE10 */
  flex-wrap: wrap;
  padding: 0 0;
  max-width: 1500px;
  margin: 0 auto;
}

.column {
  -ms-flex: 50%; /* IE10 */
  flex: 50%;
  max-width: 50%;
  padding: 0 0;
}


@media screen and (max-width: 800px) {
  .column {
    -ms-flex: 100%;
    flex: 100%;
    max-width: 100%;
  }
}

#BtnTop {
  display: none;
  position: fixed;
  bottom: 20px;
  right: 30px;
  z-index: 99;
  border: none;
  outline: none;
  background-color: red;
  color: white;
  cursor: pointer;
  padding: 15px;
  border-radius: 10px;
  font-size: 18px;
}

#BtnTop:hover {
  background-color: #555;
}