text field not working in safari

Your problem lies in calcstyle.css here:

* { 
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
}

I’m not entirely sure why user-select: none; would prevent you from typing into an input but removing this block fixes it for me.

EDIT

Here is a possible solution:

Select everything but your inputs…

*:not(input.field) {    
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
}