Generated by SassMeister.com.

gistfile1.js

(function() {
  if ( ! document.body.classList.contains('logged-in') ) {
    alert('Please log in before using this bookmarklet.  I’m too lazy to make it work for logged-out.');
  } else {
    var isVisible = false;
    if (document.body.classList.contains('borderless')) {
      window.addEventListener('scroll', function() {
        if (window.scrollY > 600 && ! isVisible ) {
          document.querySelector('.footer-wrap').style.visibility = 'visible';
          isVisible = true;
        } else if (window.scrollY <= 600 && isVisible ) {
          document.querySelector('.footer-wrap').style.visibility = 'hidden';
          isVisible = false;
        }
      });
    }
  }
})();

SassMeister-input.scss

// ----
// Sass (v3.3.7)
// Compass (v1.0.0.alpha.18)
// Bourbon (v4.0.2)
// ----

@import "bourbon/bourbon";

.logged-in {
  &.borderless {
    .footer {
      @include box-sizing(border-box);
      z-index: -2;
      height: 560px;
    }
    
    .footer-wrap {
      visibility: hidden;
      z-index: -1;
      position: fixed;
      bottom: 0;
      left: 50%;
      @include transform(translate(-50%));
    }
  }
  
  &:not(.borderless) {
    padding-bottom: 560px;
    
    .footer {
      z-index: -1;
      position: fixed;
      bottom: 0;
      width: 100%;
    }
  }
}

SassMeister-output.css

.logged-in.borderless .footer{-webkit-box-sizing:border-box;-moz-box-sizing:border-box;box-sizing:border-box;z-index:-2;height:560px}.logged-in.borderless .footer-wrap{visibility:hidden;z-index:-1;position:fixed;bottom:0;left:50%;-webkit-transform:translate(-50%);-moz-transform:translate(-50%);-ms-transform:translate(-50%);-o-transform:translate(-50%);transform:translate(-50%)}.logged-in:not(.borderless){padding-bottom:560px}.logged-in:not(.borderless) .footer{z-index:-1;position:fixed;bottom:0;width:100%}