css不确定宽高的盒子垂直居和水平居中

DOCTYPE html>
html>
    head>
        meta charset="utf-8">
        title>title>
        style type="text/css">
            .box01{
                height: 300px;        /* 这里可以改变 */
                width: 300px;        /* 这里可以改变 */
                background-color: #6676FF;
                margin: auto;
                position: absolute;
                left: 0;
                top: 0;
                bottom: 0;
                right: 0;
            }
        style>
    head>
    body>
        div class="box01">div>
    body>
html>

DOCTYPE html>
html>
    head>
        meta charset="utf-8">
        title>title>
        style type="text/css">
            .box{
                height: 100vh;
                width: 50%;
                background: #f3f300;
                display: flex;
                justify-content: center;
                align-items: center;
            }
            .box01{
                height: 300px;        /* 这里可以改变 */
                width: 300px;        /* 这里可以改变 */
                background-color: #6676FF;
            }
        style>
    head>
    body>
        div class="box">
            div class="box01">div>
        div>
    body>
html>

DOCTYPE html>
html>
    head>
        meta charset="utf-8">
        title>title>
        style type="text/css">
            .box{
                height: 100vh;
                width: 50%;
                background: #f3f300;
                display: table-cell;
                vertical-align: middle;
            }
            .box01{
                height: 300px;        /* 这里可以改变 */
                width: 300px;        /* 这里可以改变 */
                background-color: #6676FF;
                margin: 0 auto;
            }
        style>
    head>
    body>
        div class="box">
            div class="box01">div>
        div>
    body>
html>

DOCTYPE html>
html>
    head>
        meta charset="utf-8">
        title>title>
        style type="text/css">
            .box{
                height: 100vh;
                width: 50%;
                background: #f3f300;
                position: relative;
            }
            .box01{
                height: 300px;        /* 这里可以改变 */
                width: 300px;        /* 这里可以改变 */
                background-color: #6676FF;
                position: absolute;
                left: 50%;
                top: 50%;
                transform: translate(-50%,-50%);
            }
        style>
    head>
    body>
        div class="box">
            div class="box01">div>
        div>
    body>
html>