a task that I created in using gulp to easily change rem sizes based on 10px to 16px, this loop all the css and scss files and updates the measures using a regular expression, it works with calc, with 0.x .x etc

gulpfile.js

var replace = require('gulp-replace');
var gulp = require('gulp');

var js = {
    src: [
        'src/**/*.scss',
        'src/**/*.css',
        'src/**/*.tsx', //for the tsx files is in beta because it's including some strings like .remove or lorem ipsum, we need to tweak more the regexto exclude those
    ],
};

// gulp.task('default', function () {
gulp.task('default', function () { 
    return gulp.src(js.src)
      .pipe(replace(/(\d*\.?\d*)rem/gm, (item, number) => {
        return ((number * 1) * 0.625) + 'rem';
      }))
      .pipe(gulp.dest(function (file) {
        return file.base;
      }));
});