How can I set .scss variable value at runtime?

I am coding in Ionic 3, trying to develop countdown timer. I need to set .scss value at runtime. How can I do it?

.scss code

$d: 300;
$w: 20;
$interval: 2;
$rotation: 1;

&:before {
content: "";
display: block;
width: 100%;
height: 100%;
box-sizing: border-box;
border: $w+px solid #fff;
-webkit-animation-duration: $interval+s;
-webkit-animation-iteration-count: $rotation;
-webkit-animation-timing-function: linear;
-webkit-animation-fill-mode: forwards;
}


The value of interval and rotation may be anything like 1,2,3,4,etc.. How can I set it at runtime?

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