Change font sizes dynamically for a web page

dynamic-font-sizes.js

var StylingHelper = function(){
    this.id = 'dynamic-styles';
    this.step = 2;
    this.count = 1;
    this.h1Size, this.h2Size, this.h3Size, this.h4Size, this.h5Size, this.h6Size, this.pSize;

};

StylingHelper.prototype.increment = function() {
    this.count++;
    this.step = this.step + 2;
    this.updateStyling();
};

StylingHelper.prototype.decrement = function() {
    if ( this.count < 2 ) {
        return;
    }
    this.step = this.step - 2;
    this.count--;
    this.updateStyling();
};

StylingHelper.prototype.updateStyling = function() {
    var $el = $('#dynamic-styles');

    this.h1Size = 26;
    this.h2Size = 24;
    this.h3Size = 22;
    this.h4Size = 20;
    this.h5Size = 18;
    this.h6Size = 16;
    this.pSize = 19;

    if ( this.count > 1 ) {

        this.h1Size = 26 + this.step;
        this.h2Size = 24 + this.step;
        this.h3Size = 22 + this.step;
        this.h4Size = 20 + this.step;
        this.h5Size = 18 + this.step;
        this.h6Size = 16 + this.step;
        this.pSize = 19 + this.step;

    }

    $el.text(`

        .welcomeSec h1 {
            font-size: ${this.h1Size}px;
        }

        .welcomeSec h2 {
            font-size: ${this.h2Size}px;
        }

        .welcomeSec h3 {
            font-size: ${this.h3Size}px;
        }

        .welcomeSec h4 {
            font-size: ${this.h4Size}px;
        }

        .welcomeSec h5 {
            font-size: ${this.h5Size}px;
        }

        .welcomeSec h6 {
            font-size: ${this.h6Size}px;
        }

        .welcomeSec p {
            font-size: ${this.pSize}px;
        }

    `);
};

StylingHelper.prototype.init = function() {

    if( !document.getElementById(this.id) ) {
        var style = document.createElement('style');
        style.id = 'dynamic-styles';
        $('head').append(style);
    }

};

var stylingHelper = new StylingHelper();
stylingHelper.init();

$('body').on('click', '#increaseFontSize', function(event) {
    stylingHelper.increment();
});

$('body').on('click', '#decreaseFontSize', function(event) {
    stylingHelper.decrement();
});