A Pen by Long Lazuli.

index.html

<button onclick="grid.addLi()">+</button>
<button onclick="grid.removeLi()">-</button>

<ul>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
</ul>

<p>Above is a list displayed as a grid. Thanks to pseudo classes, the general sibling combinator and a Sass <code>for</code> loop, you can change the number of columns (the <code>$cols</code> variable) and items (<code>&lt;li&gt;</code>s) and it will 'self correct' to eliminate gaps. No classes; no worries. For more info on the underlying CSS involved, read <a href="http://www.heydonworks.com/article/tetris-the-power-of-css"><i>Tetris and The Power Of CSS</i></a>.</p>

script.js

var grid = {};

document.addEventListener("DOMContentLoaded", function() {
  var ul = document.getElementsByTagName('ul')[0],
      li = document.createElement('li');

  grid.addLi = function(){
    ul.appendChild(li.cloneNode(true));
  }


  grid.removeLi = function(){
    ul.removeChild(ul.lastChild);
  }
  
});

Self-Responsive-Correcting-Grid.-With-MediaQuery-No-classes!.markdown

Self Responsive Correcting Grid. With MediaQuery No classes!

Heydon did the big work. I added here a responsive solution. I don't want to have the same number of columns for each resolution.

Forked from Heydon's Pen Self Correcting Grid. No classes!.

A Pen by Long Lazuli on CodePen.

License.

style.scss

// declaration of variables
  $max-width : 1280px;
  $column-min-width: 120px;

  $max-columns: ceil( $max-width / $column-min-width ) ;


/* below is just boilerplate styles */
* {
    font-family: sans-serif;
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    padding: 1em;
    max-width: $max-width;
    margin: 0 auto;
}

p {
    margin-bottom: 1em;   
}

button,
code {
  font-family: monospace;
}

button {
  cursor: pointer;
  padding: 0 1ch;
  border: 2px solid #999;
  border-radius: 2px;
  font-weight: bold;
  background-color: #AAA;
  &:hover {
    border-color: black;
  }
  &:active {
    background-color: #666;
    color: white;
  }
  
}

* + ul {
  margin-top: 1em;
}

li {
    float: left;
    font-size: 1.5em;
    font-weight: bold;
    height: 3em;
    line-height: 3;
    border: 1px solid white;
    list-style: none;
    text-align: center;
    background: #222;
    color: #fff;
}



// choose a number of columns
@mixin liAsColumns ($cols){

  li { width: 100% / $cols; }

  @for $i from 1 through $cols {
    %divider-#{$cols}-#{$i} {
      width: 100% / $i;
    }
  }
  @if($cols > 1){

    @for $j from 1 through ( $cols - 1 ) {
      li:nth-child(#{$cols}n+1):nth-last-child(#{$j})  {
        @extend %divider-#{$cols}-#{$j};

        @if($j > 1){
          @if( $j == 2){
            & + li { @extend %divider-#{$cols}-#{$j};}
          }@else{
            & ~ li { @extend %divider-#{$cols}-#{$j};}
          }
        }
      }
    }
  }
}


/* 1 column grid : */
@include liAsColumns (1);

@for $cols from 2 through $max-columns - 1 {
  /* #{$cols} columns grid : */
  @media (min-width: ($column-min-width * $cols) + 1 )
     and (max-width: ($column-min-width * ($cols + 1) ) ){
    @include liAsColumns($cols);
  }
}

/* #{$max-columns} columns grid : */
@media (min-width: ($column-min-width * $max-columns) + 1px ) {
  @include liAsColumns($max-columns);
}