Only CSS: 404 Rolling Box

1<div class="rail"><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div><div class="stamp four">4</div><div class="stamp zero">0</div></div><div class="world"><div class="forward"><div class="box"><div class="wall"></div><div class="wall"></div><div class="wall"></div><div class="wall"></div><div class="wall"></div><div class="wall"></div></div></div></div>