Element not coming to center. I am using absolute? - html

Question

div #introbox is not centering. I have used container as relative and introbox as absolute. I have set top,bottom,left and right as 0. Still box is not centring. I want to centre the introbox in the intropic.
html,body{
padding: 0;
margin:0;
}
.container{
width: 960px;
margin:0 auto;
position: relative;
}
#header{
width: 100%;
height: 120px;
border-bottom: 1px solid black;
}
#nav{
height: 55px;
border-bottom: 4px solid lightblue ;
}
#intro-pic{
height: calc(100vh - 181px);
width: 100%;
background: url("img/introbg.jpg") center fixed;
}
#intro-box{
height: 55vh;
width: 800px;
background: rgba(0,0,0,0.74);
border-radius: 15px;
position: absolute;
top: 0px;
bottom: 0px;
right: 0px;
left:0px;
}
<div id="header">
<div class="container">
Header
</div>
</div>
<div id="nav">
<div class="container">
Nav
</div>
</div>
<div id="intro-pic">
<div class="container">
<div id="intro-box">
sdfdsfds
</div>
</div>
</div>

Answer 1

Using transform:translate will work for any size div.
html,
body {
padding: 0;
margin: 0;
height:100%;
}
.container {
width: 960px;
margin: 0 auto;
position: relative;
height:100vh;
}
#intro-box {
height: 55vh;
width: 800px;
background: rgba(0, 0, 0, 0.74);
border-radius: 15px;
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%,-50%);
/* vertical centering */
}
<div id="intro-pic">
<div class="container">
<div id="intro-box">
sdfdsfds
</div>
</div>
</div>

Answer 2

Find the below code.
Make left position 50% and give margin-left half of the wrapper width value.
#intro-box{
height: 55vh;
width: 800px;
background: rgba(0,0,0,0.74);
border-radius: 15px;
position: absolute;
top: 0px;
bottom: 0px;
left:50%;
margin-left: -400px; /* Half of the wrapper width */
}
Try below example if you are trying exact center (from top & left)
#intro-box{
height: 55vh;
width: 800px;
background: rgba(0,0,0,0.74);
border-radius: 15px;
position: absolute;
top: 50%;
left: 50%;
margin-left: -400px; /* Half of the wrapper width */
margin-top: -27.5vh; /* Half of the wrapper height*/
}
JSFIDDLE DEMO

Answer 3

#intro-box {
height: 55vh;
width: 800px;
background: rgba(0,0,0,0.74);
border-radius: 15px;
position: absolute;
left: 50%;
top: 50%;
margin-left: -400px;
margin-top: -27.5vh;
}
But again, .container should have height over or equal to #intro-box

Answer 4

There are many ways to center Elements:
using line-height:
you want to center text and you know the size of the box:
.box { background: red; height: 200px; }
.box span { display:block; text-align: center; line-height: 200px; }
<div class="box">
<span>Text</span>
</div>
using transform:
you want to center anything but dont know the size of your box:
.box, .box2 { background: red; height: 200px; }
.box span { top: 50%; text-align: center; position: relative; display: block; transform: translateY(-50%) }
.box2 span { top: 50%; left: 50%; position: relative; display: inline-block; transform: translate(-50%, -50%) }
<div class="box">
<span>Text</span>
</div>
OR WITHOUT TEXT-ALIGN:
<div class="box2">
<span>Text</span>
</div>
using absolute position:
you know the height of the element you want to center
.box, .box2 { background: red; height: 200px; position: relative; width: 100%; }
.box span { position: absolute; background: green; height: 50px; width: 50px; top: 50%; left: 50%; margin: -25px 0 0 -25px; }
<div class="box">
<span></span>
</div>
There are even more ways to manage this.