#time_span, h1, h2 {
   color: black;
 }
 
 .center {
 text-align: center;
 }
 
 #time_span {
 margin-top: 0px;
 }
 
 * {box-sizing: border-box}
 
 body, html {
   height: 100%;
   margin: 0;
   font-family: Arial;
 }
 
 .tablink {
   background-color: #555;
   color: white;
   float: left;
   border: none;
   outline: none;
   cursor: pointer;
   padding: 14px 16px;
   font-size: 17px;
   width: 25%;
   text-align: center;
   text-decoration: none;
 }
 
 .tc:hover {
   background-color: red;
 }
 
 .ta:hover {
   background-color: blue;
 }
 
 .tt:hover {
   background-color: green;
 }
 
 .ts:hover {
   background-color: orange;
 }

 .tabcontent {
   color: white;
   display: none;
   padding: 100px 20px;
   padding-bottom: 0px;
 }
 
 #clock {
   padding-top: 50px;
 }
 
 .dbl {
   font-size: 4em;
 }
 
 .mt-0 {
   margin-top: 0px;
 }
 
 .mb-0 {
   margin-bottom: 0px;
 }