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

body {
  background-color: #f5f5f5;
  display: flex;
  padding: 20px 0;
  flex-direction: column;
  align-items: center;
  row-gap: 20px;
}

.container {
  display: flex;
  padding: 10px;
  width: 80%;
  background: #ddd;
}

.item {
  height: 50px;
  width: 50px;
  border: 3px solid #333;
}
.item:nth-child(3n + 1) {
  background: #eb6a5f;
  border-color: #832219;
}
.item:nth-child(3n + 2) {
  background: #f5bd4f;
  border-color: #785716;
}
.item:nth-child(3n + 3) {
  background: #61c454;
  border-color: #206a16;
}

.container1 {
  height: 300px;
}
.container1 .item {
  margin: auto;
}

.container2 .item:nth-child(3) {
  margin-left: auto;
}

.container3 .item:nth-child(3) {
  margin-left: auto;
}

.container4 .item:nth-child(3) {
  margin: 0 auto;
}

.container5 {
  flex-wrap: wrap;
}
.container5 .item {
  --n: 7;
  margin: 10px calc((100% - var(--n) * 50px) / var(--n) / 2);
}