header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 12px 16px;
  color: #ccc;
  font-size: 0.95rem;
  letter-spacing: 0.04em;
}

*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

span {
  font-size: 30px;
}

body {
  background: #111;
  font-family: sans-serif;
  padding: 16px;
}

#gallery {
  margin: 0 auto;
  max-width: 1400px;
}

.grid-sizer,
.grid-item {
  width: calc(25% - 12px);
}

.grid-item {
  margin-bottom: 16px;
  overflow: hidden;
  border-radius: 4px;
  background: #222;
}

.grid-item img {
  display: block;
  width: 100%;
  height: auto;
  transition: opacity 0.3s;
}

.grid-item img.loading {
  opacity: 0;
}

@media (max-width: 1100px) {
  .grid-sizer,
  .grid-item { width: calc(33.333% - 11px); }
}

@media (max-width: 750px) {
  .grid-sizer,
  .grid-item { width: calc(50% - 8px); }
}

@media (max-width: 480px) {
  .grid-sizer,
  .grid-item { width: 100%; }
}