<div class="buttons-ctn">
  <a href="" class="button button--left"><span>Left</span></a>
  <a href="" class="button button--right"><span>Right</span></a>
</div>
<div class="button__content button__content--left">
  <h2>You chose left!</h2>
  <a href="">Signup for nothing here</a>
</div>
<div class="button__content button__content--right">
  <h2>You chose right!</h2>
  <a href="">Signup for nothing here</a>
</div>

<main>
  <h1><a href="http://ettrics.com">Ettrics</a></h1>
  <p>Shifting Material Button Modal</p>
  <p><a href="http://ettrics.com/code/shifting-material-button-modal/" target="_blank">Read article on Ettrics.com</a></p>
</main>
@mixin easeOut {
  transition: all .35s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

$black: lighten(black, 8);

* {
  box-sizing: border-box;
}

body {
  background: #38c5b9;
  font-family: 'Montserrat';
  font-weight: 300;
  line-height: 1.5;
}

a {
  text-decoration: none;
  color: inherit;
}

.buttons-ctn {
  will-change: transform;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -140px;
  margin-top: -30px;
  transform-style: preserve-3d;
  backface-visibility: hidden;
}

.button {
  will-change: transform;
  position: relative;
  float: left;
  display: inline-block;
  padding: 20px;
  width: 140px;
  text-align: center;
  line-height: normal;
  @include easeOut;
  
  &--left {
    background: $black;
    color: white;
  }
  
  &--right {
    background: darken(white, 8);
    color: $black;
  }
  
  &--active {
   cursor: default;
    
   span {
     opacity: 0;
    }
  }
}

.button__content {
  display: block;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  padding: 60px 20px;
  text-align: center;
  width: 600px;
  visibility: hidden;
  opacity: 0;
  z-index: 10;
  color: white;
  
  &--left {
    color: white;
    
    a {
      color: $black;
      background: white;
    }
  }
  
  &--right {
    color: $black;
    
    a {
      color: white;
      background: $black;
    }
  }
  
  &--active {
    opacity: 1;
    visibility: visible;
  }
  
  a {
    display: inline-block;
    padding: 10px 20px;
  }
  
  h2 {
    font-size: 36px;
    text-transform: uppercase;
    letter-spacing: 3px;
    font-weight: 300;
  }
  
  @media (max-width: 650px) {
    width: 295px;
  }
}

main {
  color: white;
  text-align: center;
  h1 {
    font-weight: 300;
    margin-bottom: 8px;
    margin-top: 24px;
  }
  
  p {
    margin-top: 0;
    
    a {
      font-size: 20px;
      position: absolute;
      left: 0;
      right: 0;
      bottom: 24px;
      color: rgba(black, 0.6);
    }
  } 
}
View Compiled
var button 			= $('.button');
var content 		= $('.button__content');
var win 				= $(window);

var expand = function() {
  if (button.hasClass('button--active')) {
    return false;
  } else {
    var W 					= win.width();
    var xc 					= W / 2;

    var that 				= $(this);
    var thatWidth 	= that.innerWidth() / 2;
    var thatOffset 	= that.offset();
    var thatIndex		= that.index();
    var other;

    if (!that.next().is('.button')) {
      other = that.prev();
    } else {
      other = that.next();
    }

    var otherWidth		= other.innerWidth() / 2;
    var otherOffset		= other.offset();

    // content box stuff
    var thatContent = $('.button__content').eq(thatIndex);
    var thatContentW = thatContent.innerWidth();
    var thatContentH = thatContent.innerHeight();

    // transform values for button
    var thatTransX 	= xc - thatOffset.left - thatWidth;
    var otherTransX	= xc - otherOffset.left - otherWidth;
    var thatScaleX	= thatContentW / that.innerWidth();
    var thatScaleY	= thatContentH / that.innerHeight();

    that.css({
      'z-index': '2',
      'transform': 'translateX(' + thatTransX + 'px)'
    });

    other.css({
      'z-index': '0',
      'opacity': '0',
      'transition-delay': '0.05s',
      'transform': 'translateX(' + otherTransX + 'px)'
    });

    that.on('transitionend webkitTransitionEnd', function() {
      that.css({
        'transform': 'translateX(' + thatTransX + 'px) scale(' + thatScaleX +',' + thatScaleY + ')',
      });

      that.addClass('button--active');
      thatContent.addClass('button__content--active');
      thatContent.css('transition', 'all 1s 0.1s cubic-bezier(0.23, 1, 0.32, 1)');
      that.off('transitionend webkitTransitionEnd');
    });

    return false;
  }
};

var hide = function(e) {
  var target= $(e.target);
  if (target.is(content)) {
    return;
  } else {
    button.removeAttr('style').removeClass('button--active');
    content.removeClass('button__content--active').css('transition', 'all 0.2s 0 cubic-bezier(0.23, 1, 0.32, 1)');
  }
};

var bindActions = function() {
  button.on('click', expand);
  win.on('click', hide);
};

var init = function() {
  bindActions();
};

init();

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js