/* (A) WHOLE PAGE */
* { box-sizing: border-box; }
body { background: #eee; }
 
/* (B) GALLERY WRAPPER */
.gallery {
  /* (B1) GRID LAYOUT - 3 IMAGES PER ROW */
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-gap: 20px;
 
  /* (B2) OPTIONAL WIDTH RESTRICT */
  max-width: 1000px;
  margin: 0 auto;
  overflow: hidden;
}