body {
  background-color: rgb(255, 255, 255);
}

h1 {
    color: darkcyan;
    text-align: center;
}

table {
  margin: auto;
  
}

.hydrogen {
    background-color: lightgreen;
    color: white;
}

.alkali {
  background-color: red;
  color: white;
}

.noblegas {
    background-color: cyan;
    color: white;
}

.alkalineearthmetal {
    background-color: orange;
    color: white;
}

.polyatomicmetal {
    background-color: aquamarine;
    color: white;
}

.diatomicnonmetal {
    background-color: green;
    color: white;
}

.transitionmetal {
    background-color: blue;
    color: white;
}

.posttransitionmetal {
    background-color: darkcyan;
    color : white
}

.lanthanoids {
    background-color: rgb(105, 0, 105);
    color: white
}

.unknownchemicalproperties {
    background-color: gray;
    color: white;
}

.actinide {
    background-color: rgb(143, 63, 103);
    color: white;
}

.metalloid {
    background-color: brown;
    color: white;
}

.back-btn {
  position: fixed;
  bottom: 20px;
  right: 20px;

  padding: 10px 15px;
  background-color: #333;
  color: white;
  border: none;
  border-radius: 6px;
  cursor: pointer;
}

.gap {
  height: 20px;
}

.gap td {
  border: none;
  padding: 0;
}