水平垂直居中

定位(absolute) + 负margin

.wp {
    position: relative;
}
.box {
    position: absolute;;
    top: 50%;
    left: 50%;
    margin-left: -50px;
    margin-top: -50px;
}

Demo 演示

<div class="wp">
    <div class="box size">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

.box.size{
    width: 100px;
    height: 100px;
}

/* ======================== */

.wp {
    position: relative;
}
.box {
    position: absolute;;
    top: 50%;
    left: 50%;
    margin-left: -50px;
    margin-top: -50px;
}

定位(absolute) + margin auto

.wp {
    position: relative;
}
.box {
    position: absolute;;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    margin: auto;
}

Demo 演示

<div class="wp">
    <div class="box size">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

.box.size{
    width: 100px;
    height: 100px;
}
/* ======================== */

.wp {
    position: relative;
}
.box {
    position: absolute;;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    margin: auto;
}

定位(absolute) + calc

.wp {
    position: relative;
}
.box {
    position: absolute;;
    top: calc(50% - 50px);
    left: calc(50% - 50px);
}

Demo 演示

<div class="wp">
    <div class="box size">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

.box.size{
    width: 100px;
    height: 100px;
}
/* ======================== */

.wp {
    position: relative;
}
.box {
    position: absolute;;
    top: calc(50% - 50px);
    left: calc(50% - 50px);
}

定位(absolute) + transform

.wp {
    position: relative;
}
.box {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

Demo 演示

<div class="wp">
    <div class="box">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

/* ======================== */

.wp {
    position: relative;
}
.box {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

flex

.wp {
    display: flex;
    justify-content: center;
    align-items: center;
}

Demo 演示

<div class="wp">
    <div class="box">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

/* ======================== */

.wp {
    display: flex;
    justify-content: center;
    align-items: center;
}

flex + margin

.wp {
    display: flex;
}
.box {
    margin: auto;
}

Demo 演示

<div class="wp">
    <div class="box">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

/* ======================== */

.wp {
    display: flex;
}

.box {
    margin: auto;
}

lineheight

.wp {
    line-height: 300px;
    text-align: center;
    font-size: 0px;
}
.box {
    font-size: 16px;
    display: inline-block;
    vertical-align: middle;
    line-height: initial;
    text-align: left; /* 修正文字 */
}

Demo 演示

<div class="wp">
    <div class="box">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

/* ======================== */

.wp {
    line-height: 300px;
    text-align: center;
    font-size: 0px;
}
.box {
    font-size: 16px;
    display: inline-block;
    vertical-align: middle;
    line-height: initial;
    text-align: left; /* 修正文字 */
}

table

<table>
    <tbody>
        <tr>
            <td class="wp">
                <div class="box">123123</div>
            </td>
        </tr>
    </tbody>
</table>

.wp {
    text-align: center;
}
.box {
    display: inline-block;
}

Demo 演示

<table>
    <tbody>
        <tr>
            <td class="wp">
                <div class="box">123123</div>
            </td>
        </tr>
    </tbody>
</table>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

/* ======================== */

.wp {
    text-align: center;
}
.box {
    display: inline-block;
}

css-table

.wp {
    display: table-cell;
    text-align: center;
    vertical-align: middle;
}
.box {
    display: inline-block;
}

Demo 演示

<div class="wp">
    <div class="box">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

/* ======================== */

.wp {
    display: table-cell;
    text-align: center;
    vertical-align: middle;
}
.box {
    display: inline-block;
}

grid

.wp {
    display: grid;
}
.box {
    align-self: center;
    justify-self: center;
}

Demo 演示

<div class="wp">
    <div class="box">123123</div>
</div>

.wp {
    border: 1px solid red;
    width: 300px;
    height: 300px;
}

.box {
    background: green;
}

/* ======================== */

.wp {
    display: grid;
}
.box {
    align-self: center;
    justify-self: center;
}