body {
  background-color: black;
  color: white;
  font-family: Arial, sans-serif;
  font-size: medium;
}

/* Main and footer */
a {
  color: white;
  text-decoration: none;
}

a:hover {
  color: #d0d080;
}

.main {
  text-align: center;
}

.verticalspace {
  padding-top: 3em;
  padding-bottom: 3em;
}

.verticalspaceafterheader {
  padding-bottom: 3em;
}

.textbox {
  margin-left: auto;
  margin-right: auto;
  text-align: center;
  width: 65%
}

/* Image collections */
.row {
  display: flex;
  flex-wrap: wrap;
  padding: 0 4px;

  margin-left: auto;
  margin-right: auto;
  text-align: center;
  width: 85%
}

.column {  /* Four columns as default */
  flex: 24%;
  max-width: 24%;
  padding: 0 4px;
}

.column img {
  margin-top: 8px;
  vertical-align: middle;
  width: 100%;
}

@media screen and (max-width: 800px) {  /* Two columns */
.column {
    flex: 47%;
    max-width: 47%;
  }
}

@media screen and (max-width: 600px) {  /* One column */
.column {
    flex: 95%;
    max-width: 96.5%;
  }
}