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#parent {position: relative;}
#child {
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
width: 50%;
height: 30%;
margin: auto;
}
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/* Flex */
.center {
display: flex;
justify-content: center;
align-items: center;
}
/* Without Flex */
.parent {
position: relative;
}
.child {
position: absolute;
top: 50%;
transform: translateY(-50%);
}
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HTML:
<div class="ext-box">
<div class="int-box">
<h2>Some txt</h2>
<p>bla bla bla</p>
</div>
</div>
CSS:
div.ext-box { display: table; height: 100%; width:100%;}
div.int-box { display: table-cell; vertical-align: middle; }