CSS: vertical centering

display: table

.table {
  display: table;
  width: 100%;
}

.table div {
  display: table-cell;
  vertical-align: middle;
}

<div class="table">
  <div>
    <!-- conteúdo -->
  </div>
</div>

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position: absolute

.relative {
  position: relative;
}

.absolute {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
}

<div class="relative">
  <div class="absolute">
    <!-- conteúdo -->
  </div>
</div>

display: flex

.flex {
  display: flex;
  align-items: center;
}

<div class="flex">
  <!-- conteúdo -->
</div>

display: grid

.grid {
  display: grid;
  place-items: center;
}

<div class="grid">
  <div>
    <!-- conteúdo -->
  </div>
</div>

margin: auto

.margin {
  display: flex;
}

.margin div {
  margin: auto;
}

<div class="margin">
  <div>
    <!-- conteúdo -->
  </div>
</div>