try jQuery by Code school / Styling / Animation

animation.js

//5.8 Animate I, 5.9 Animate II, 5.10 Animation Speed, 5.11 Animate III
$(document).ready(function() {
  $('.tour').on('mouseenter', function() {
    $(this).addClass('highlight');
    $(this).find('.per-night').animate({'top': '-14px', 'opacity': '1'}, 'fast'); //adding one more key/value to this object representing a top of -14px
  });
  $('.tour').on('mouseleave', function() {
    $(this).removeClass('highlight');
    $(this).find('.per-night').animate({'top': '0px', 'opacity': '0'}, 'fast');
  });
});

zpartOf.html

<div id="all-tours">
  <h1>Guided Tours</h1>
  <ul>
    <li class="tour usa">
      <h2>New York, New York</h2>
      <span class="details">$1,899 for 7 nights</span>
      <span class="per-night"><span class="price">$275</span>/night</span>
      <button class="book">Book Now</button>
      <ul class="photos">
        <li>
          <img src="/assets/photos/newyork1.jpg">
          <span>Notre Dame de Paris</span>
        </li>
      </ul>
    </li>
    <li class="tour france" data-discount="99">
      <h2>Paris, France</h2>
      <span class="details">$1,499 for 5 nights</span>
      <span class="per-night"><span class="price">$300</span>/night</span>
      <button class="book">Book Now</button>
      <ul class="photos">
        <li>
          <img src="/assets/photos/paris3.jpg">
          <span>Brooklyn Bridge</span>
        </li>
      </ul>
    </li>
    <li class="tour uk" data-discount="149">
      <h2>London, UK</h2>
      <span class="details">$2,199 for 5 nights</span>
      <span class="per-night"><span class="price">$440</span>/night</span>
      <button class="book">Book Now</button>
      <ul class="photos">
        <li>
          <img src="/assets/photos/london.jpg">
          <span>Tower of London</span>
        </li>
      </ul>
    </li>
  </ul>
</div>

• Let's update our mouseleave handler to remove the .per-night price with a little style. Animate the price to a top of 0px and an opacity of 0 when the mouse leaves the .tour element, and make it happen with a 'fast' duration.