Edit in JSFiddle

<div class="parent">
    <div class="element">
        I'm bang in the center!
    </div>
</div>

/* variables */

/* colours */
$grey: rgba(220, 231, 235, 1);
$lightgrey: rgba(220, 231, 235, 0.25);
$blue: rgba(34, 190, 198, 1);
$white: rgba(255, 255, 255, 1);

/* fonts */
$sans: 'Ubuntu', sans-serif;
$heading: 'Source Sans Pro', sans-serif;

body {
    background: $grey;
    font-family: 'Ubuntu', sans-serif;
	color: $white;
}

/* parent */
.parent {
    position: relative;
    background: $grey;
    width: 100%;
    height: 100vh;
}

/* class to center element */
.center-me {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

/* element to be centered */
.element {
    @extend .center-me;
    background: $blue;
    padding: 5%;
}