body {
  font-family: Helvetica;
  font-size: 16px;
  line-height: 1.5;
  color: #444444;
  margin: 50px auto 100px auto;
  max-width: 800px;
  text-align: center;
}

header {
  margin: 0 0 50px 0;
}

h1 {
  font-size: 48px;
  line-height: 1.3;
  margin: 0;
}

h2 {
  font-size: 14px;
  font-weight: 400;
  margin: 0;
}

.photos {
  display: flex;
  flex-wrap: wrap;
  padding: 0 20px;
}

a {
  width: 50%;
  padding: 10px;
  transition: border-color 0.5s;
}

a.clicked {
  border: 5px solid #ff4141;
}

.modal-background {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.75);
}

.modal-close {
  position: fixed;
  right: 0;
  top: 0;
  color: white;
  padding: 20px 25px;
  cursor: pointer;
}

.modal-content {
  position: fixed;
  top: 50%;
  left: 50%;
  max-width: 760px;
  width: 90%;
  transform: translate(-50%, -50%);
}

.modal {
  display: none;
}

@media (max-width: 520px) {

.photos a {
  width: 100%;
  padding: 0;
  margin-bottom: 20px;
}

}