I just wanted to post an example of how my CSS looks in a post-preprocessor world.

A "Modern" CSS File

// imports
@import 'normalize.less';
@import 'grid.less';
@import 'helpers.less';
@import 'mixins.less';

// brand colors
@red: hsl(6, 89%, 59%);
@light_gray: hsl(0, 0%, 93%);

// apply a natural box layout model to all elements
* { -moz-box-sizing: border-box; -webkit-box-sizing: border-box; box-sizing: border-box; }

// class for showing certain elements only on mobile
.mobile { display: none; }

// structure
body {
  color: #000;
  font: 13px/1.4 'adobe-garamond-pro', Times, serif;
  padding: 0 2em;
}
select, input, textarea {
  color: #444;
  font-family: Arial, sans-serif;
}
#page {
  padding-top: 100px;
}
.row {
  position: relative;
}

// logo
.site-title {
  margin: 0;
}
.logo {
  display: block;
  img {
    display: block;
    height: auto;
  }
}
.animation {
  width: 165px; // *shudder*
  height: auto;
  margin-top: 16px;
}

// nav
.navbar {
  position: absolute;
  top: 2em;
  right: 0;
  height: 100px;
}
.main-nav {
  ul {
    position: relative;
    float: left;
    padding: 0;
    margin: 2px 1em 10px 0;
  }
  li {
    float: left;
    margin: 0 1em;
  }
  a {
    display: block;
    color: black;
    text-decoration: none;
    font-size: 140%;
    line-height: 1.1;
    border-bottom: 2px solid transparent;
    &:hover,
    &.menuactive {
      border-color: @red;
    }
  }
  .searchform {
    float: left;
  }
}
.sub-nav {
  ul {
    float: left;
    min-width: 200px;
    height: 2em;
    line-height: 2em;
    background: @light_gray;
    margin: 0 0 1em 0;
    padding: 0 1em;
    li {
      float: left;
    }
    a {
      color: black;
      text-decoration: none;
    }
    a.menuactive {
      color: @red;
    }
  }
}

// search
.searchform {
  input {
    float: left;
    height: 23px;
    outline: none;
  }
  input[type=search] {
    padding: 0 .5em;
    width: 180px;
    background-color: @light_gray;
    border: none;
    box-shadow:
      inset 1px 1px 2px rgba(0,0,0,0.38);
    font-size: 12px;
  }
  input[type=submit] {
    background: url(../img/mag-glass.png) no-repeat;
    width: 26px;
  }
}

// content
h1, .h1 {
  color: @red;
  font-size: 150%;
  font-weight: normal;
}
h2, .h2 {
  font-size: 115%;
}
h3, .h3 {
  font-size: 100%;
}
h4, .h4 {
  font-size: 80%;
}
h2 + h3 {
  margin-top: -1em;
  font-weight: normal;
  font-style: italic;
}
.content {
  background: url(../img/homes-strip.png) no-repeat right top;
  min-height: 500px;
  padding: 0 20% 2em 5%;
}
.page-title {
  margin-top: 0;
}

// footer
.footer {
  margin: 2em 0;
  border-top: 3px solid @red;
  .vcard {
    float: left;
    i {
      font-style: normal;
    }
  }
  .copyright {
    float: right;
  }
}

// small screen
@media handheld, only screen and (max-width: 800px) {
  body {
    font-size: 16px;
    padding: 0 1em;
  }
  .mobile {
    display: block;
  }
  #page {
    padding-top: 20px;
  }
  .content {
    padding-left: 0;
  }
  // branding & nav
  #branding {
    position: relative;
    height: 140px;
    padding-left: 190px;
  }
  .animation {
    position: absolute;
    top: 0;
    left: 0;
    margin: 0;
  }
  .site-title {
    padding-top: 4px;
  }
  .navbar {
    position: static;
    height: auto;
  }
  .main-nav {
    position: absolute;
    top: 83px;
    left: 186px;
    li {
      margin: 0 1em 0 0;
    }
    a {
      font-size: 120%;
    }
  }
  .sub-nav ul {
    float: none;
  }
  // content
  .page-title {
    padding-top: .5em;
    border-top: 3px solid @light_gray;
  }
  // footer
  .footer {
    font-size: 80%;
    p {
      float: none !important;
    }
  }
  // grid adjustments
  .row, .container {
    width: 100%;
    min-width: 0;
    margin-left: 0;
    margin-right: 0;
    padding-left: 0;
    padding-right: 0;
  }  
  .row .span1, .row .span2, .row .span3, .row .span4, .row .span5, .row .span6, .row .span7, .row .span8, .row .span9, .row .span10, .row .span11, .row .span12, .row .span13, .row .span14, .row .span15, .row .span16, .row .span17, .row .span18, .row .span19, .row .span20, .row .span21, .row .span22, .row .span23, .row .span24
  {
    width: auto;
    float: none;
    margin-left: 0;
    margin-right: 0;
    padding-left: 0;
    padding-right: 0;
  }
}

// mobile
@media handheld, only screen and (max-width: 639px) {
  // branding & nav
  #branding {
    padding-left: 95px;
    height: 80px;
  }
  .logo .animation {
    width: auto;
    height: 60px;
  }
  .main-nav {
    position: static;
    li {
      margin: 0 1em .5em 0;
    }
  }
  .searchform {
    display: none;
  }
  .content {
    padding: 0;
    min-height: 0;
    background: none;
  }
}