.center {text-align: center;}
.left {text-align: left;}
.right {text-align: right;} 
.justify {text-align: justify;} 
.serif {font-family: "Times New Roman", Times, serif;}
.bold {font-weight: bold;}

.black {color: black;}

a:link {
    color: black;
    background-color: transparent;
    text-decoration: underline;
  }
  
  a:visited {
    color: slategrey;
    background-color: transparent;
    text-decoration: underline;
  }
  
  a:hover {
    color: red;
    background-color: transparent;
    text-decoration: underline;
  }
  
  a:active {
    color: yellow;
    background-color: transparent;
    text-decoration: underline;
  }



  .collapsible {
    
    color: black;
    font-weight: bold;
    cursor: pointer;
    padding: 18px;
    width: 100%;
    border: none;
    text-align: left;
    outline: none;
    font-size: 15px;
  }
  
  .active, .collapsible:hover {
    background-color: #555;
  }
  
  .content {
    padding: 0 18px;
    display: none;
    overflow: hidden;
    background-color: #f1f1f1;
  }