Box horizontal vertical center layout (summary)

Catalog

1.flex Layout

2. inline-block（ Only approximate when vertically centered , Imprecise ！！！）

3. Absolute positioning + 2D transformation

4. Absolute positioning + margin: auto

5. table

---

1.flex Layout

.box {
  margin: 100px auto;
  width: 300px;
  height: 300px;
  border: 1px solid black;
  display: flex;
  justify-content: center;
  align-items: center;
}
.child {
  width: 50px;
  height: 50px;
  background-color: pink;
}

    <div class="box">
        <div class="child"></div>
    </div>

2. inline-block（ Only approximate when vertically centered , Imprecise ！！！）

.box {
  margin: 100px auto;
  width: 300px;
  height: 300px;
  border: 1px solid black;
  text-align: center;
  line-height: 300px;
}
.child {
  display: inline-block;
  width: 50px;
  height: 50px;
  background-color: pink;
  vertical-align: middle;
}

    <!-- 
         to child Set up display: inline-block; hold child Become a box in the line , It can be regarded as img Label settings text-align: center; Horizontal center 
         Then increase the height of the parent box line-height: 300px; Sub box baseline alignment 
     -->
    <div class="box">
        <div class="child"></div>
    </div>

3. Absolute positioning + 2D transformation

        .box {
            position: relative;
            margin: 100px auto;
            width: 300px;
            height: 300px;
            border: 1px solid black;
        }
        .child {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            width: 50px;
            height: 50px;
            background-color: pink;
        }

    <div class="box">
        <div class="child"></div>
    </div>

4. Absolute positioning + margin: auto

Just want to center horizontally right:0; left: 0;

        .box {
            position: relative;
            margin: 100px auto;
            width: 300px;
            height: 300px;
            border: 1px solid black;
        }
        .child {
            position: absolute;
            top: 0;
            left: 0;
            bottom: 0;
            right: 0;
            margin: auto;
            width: 50px;
            height: 50px;
            background-color: pink;
        }

    <div class="box">
        <div class="child"></div>
    </div>

5. table

Just want to center horizontally child Inside margin: 0 auto; Get rid of

.box {
  margin: 100px auto;
  width: 300px;
  height: 300px;
  border: 1px solid black;
  display: table-cell;    // The small square in the table 
  vertical-align: middle;  // Cannot be used for block level elements , It can only act on inline elements and inline blocks . It's special here .
}
.child {
  margin: 0 auto;
  width: 50px;
  height: 50px;
  background-color: pink;
}

    <!-- 
         Why does the parent box run ?
        display: table-cell; After setting, the parent box is no longer a block element , therefore margin: 100px auto; It doesn't work 
     -->
    <div class="box">
        <div class="child"></div>
    </div>