App in wordpress doesnt fit to mobile screen

The best approach would be as toscho said in the comments – to write your own script an make it mobile friendly from the start. But if you want a quick, temporary solution you could do something like this:

<div id="maincontainerWrapper" style="overflow: auto;">
    <div id="maincontainer" style="position: relative;">
          ...
    </div>
</div>

then your calculator app will be accessible in full width by dragging it left and right which would be uncomfortable and unintuitive for your users.