table {
  margin: auto;
  margin-top: 20px;
  width: 80%;
  border: 10px solid transparent;
}
td {
  width: 25%;
  position: relative;
  border: 10px solid transparent;
}
td:after {
  content: '';
  display: block;
  margin-top: 100%;
}
td .content {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  background-color: #CCC;
}
td .valid {
  background-color: #65a3d0;
}



body {
  background-color: #333333;
  font-family: 'helvetica', sans-serif;
  font-size: 16px;
  margin: 0;
  padding: 0;
  background: -webkit-linear-gradient(225deg, #333333 0%, #b65959 100%);
  background: linear-gradient(45deg, #333333 0%, #b65959 100%);
  filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#999999', endColorstr='#e8e8e8',GradientType=1 );
}

.container-fluid {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  background-color: transparent;
}

.element-card {
  /* float: left; */
  width: 100px;
  height: 130px;
  -webkit-transform-style: preserve-3d;
          transform-style: preserve-3d;
  -webkit-transform: rotatey(0deg) translatex(0px) translatey(0px);
          transform: rotatey(0deg) translatex(0px) translatey(0px);
  -webkit-transition: all 0.6s cubic-bezier(0.68, -0.55, 0.265, 1.55);
  transition: all 0.6s cubic-bezier(0.68, -0.55, 0.265, 1.55);
  box-shadow: 4px 4px 20px rgba(0, 0, 0, 0.4);
  margin: 5px;
  cursor: pointer;
}
.mark1 .front-facing {
  background-color: #ecf0f1;
}
.mark2 .front-facing {
  background-color: #eeecf1;
}
.mark3 .front-facing {
  background-color: #f2f0ed;
}
.mark1:hover .front-facing {
  background-color: #d5eef4;
  /* -webkit-transform: rotatey(45deg) translatex(0px) translatey(0px);
          transform: rotatey(45deg) translatex(0px) translatey(0px); */
}
.mark2:hover .front-facing {
  background-color: #e5d5f5;
}
.mark3:hover .front-facing {
  background-color: #f5e6d5;
}
.mark1 {
  color: #3498db;
}
.mark2 {
  color: #8835db;
}
.mark3 {
  color: #db8f35;
}

.element-card.open {
  width: 200px;
  height: 260px;
  -webkit-transform: rotatey(-180deg) translatex(0px) translatey(0px);
          transform: rotatey(-180deg) translatex(0px) translatey(0px);
}
.element-card .front-facing {
  -webkit-transform: rotateY(0deg) translateZ(2px);
          transform: rotateY(0deg) translateZ(2px);
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  border: 2px white solid;
  border-radius: 5px;
}
.element-card .front-facing .abr {
  width: 100%;
  position: absolute;
  top: 50%;
  left: 0;
  font-size: 42px;
  margin: -35px 0 0 0;
  text-align: center;
}
.element-card .front-facing .title {
  width: 100%;
  position: absolute;
  top: 50%;
  left: 0;
  text-transform: uppercase;
  font-size: 12px;
  margin: 15px 0 0 0;
  text-align: center;
}
.element-card .front-facing .atomic-number {
  position: absolute;
  top: 5px;
  left: 5px;
  font-size: 18px;
}
.element-card .front-facing .atomic-mass {
  position: absolute;
  bottom: 10px;
  right: 10px;
  font-size: 12px;
  color: #2980b9;
}
.element-card .back-facing {
  -webkit-transform: rotateY(180deg) translateZ(0px);
          transform: rotateY(180deg) translateZ(0px);
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-orient: vertical;
  -webkit-box-direction: normal;
      -ms-flex-direction: column;
          flex-direction: column;
  -ms-flex-wrap: nowrap;
      flex-wrap: nowrap;
  -webkit-box-pack: center;
      -ms-flex-pack: center;
          justify-content: center;
  -webkit-box-align: center;
      -ms-flex-align: center;
          align-items: center;
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  background-color: #ecf0f1;
  border: 2px white solid;
  border-radius: 5px;
  padding: 20px;
  text-align: center;
  overflow: hidden;
}
.element-card .back-facing p {
  font-size: 14px;
  margin: 0;
}
.element-card .back-facing a.btn {
  display: inline-block;
  background-color: white;
  padding: 5px 15px;
  margin: 20px 0 0 0;
  color: #eee;
  background-color: #3498db;
  text-decoration: none;
  border-radius: 3px;
}
.element-card .back-facing a.btn:hover, .element-card .back-facing a.btn:focus {
  color: #fff;
  background-color: #2980b9;
}


.notice {
    padding: 15px;
    background-color: #fafafa;
    border-left: 6px solid #7f7f84;
    margin-bottom: 10px;
    -webkit-box-shadow: 0 5px 8px -6px rgba(0,0,0,.2);
       -moz-box-shadow: 0 5px 8px -6px rgba(0,0,0,.2);
            box-shadow: 0 5px 8px -6px rgba(0,0,0,.2);
}
.notice-lg {
    /* padding: 35px; */
    font-size: large;
}




.btn-circle {
  width: 30px;
  height: 30px;
  text-align: center;
  padding: 6px 0;
  font-size: 12px;
  line-height: 1.428571429;
  border-radius: 50%;
}
.btn-circle.btn-lg {
  width: 50px;
  height: 50px;
  padding: 10px 16px;
  font-size: 18px;
  line-height: 1.33;
  border-radius: 25px;
}
.btn-circle.btn-xl {
  width: 70px;
  height: 70px;
  padding: 10px 16px;
  font-size: 38px;
  line-height: 1.33;
  border-radius: 35px;
}