style.css

body, html {
   font-family: Helvetica;
   font-size: 13px;
   color: #555;
   background: #2c3e50;
}
span {
   display: inline-block;
   box-shadow: inset 0 0 1px rgba(0, 0, 0, 0.3);
}
label {
   float: left;
}
ul {
   padding: 0;
   margin: 0;
}

.msg {
  position: absolute;
  display: table;
  top: 0; left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.5);
  color: #fff;
  font-weight: bold;
  font-size: 20px;
}
.msg p {
  display: table-cell;
  vertical-align: middle;
  text-align: center;
}
.grid {
   background: #34495e;
   position: relative;
   float: left;
}
.panel {
   position: relative;
   float: left;
   margin: 0 8px;
}
.next, .stats {
   padding: 15px;
   background: #34495e;
   margin-bottom: 8px;
   color: #fff;
}
.new_game {
  color: #fff;
  text-align: center;
  padding: 10px;
  background:  #1abc9c;
  cursor: pointer;
}
.empty {
   transition: all 0.2s ease;
   position: absolute;
}
.L {
   background: #1abc9c;
}
.O {
   background: #2ecc71;
}
.S {
   background: #3498db;
}
.Z {
   background: #9b59b6;
}
.I {
   background: #f1c40f;
}
.J {
   background: #e67e22;
}
.T {
   background: #e74c3c;
}

.archive {
   background: #7f8c8d;
}

.transparent {
   background: transparent;
   box-shadow: none;
}