FABs size %

Ionic Framework ionic-v3
1

Hi,
I want to use fabs button.

variable.scss

$fab-size: 100px;
$fab-list-button-background-color:#f4f4f4;
$fab-mini-size:70px;

But screen is bigger thats problem.So I want use %50 vs but dont allow.
what can I do?
Thanks