文本居中对齐

.a{
    width: 100px;
    height: 300px;
    background-color: #286090;
}
.a div{
    width: 50px;
    height: 50px;
    background-color: aqua;
    text-align: center;
}

<div class="a">
    <div>文本居中对齐</div>
</div>