Flexbox と Grid で Div を中央寄せ

/* Center with Flexbox (most common) */
.center-flex {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
}

/* Center with Grid */
.center-grid {
  display: grid;
  place-items: center;
}

/* Center absolutely positioned element */
.center-abs {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

/* Center text horizontally */
.center-text {
  text-align: center;
}