button {
   position: fixed;
   bottom: 0;
   left: 50%;
   border: none;
   font-size: 3em;
   font-weight: bold;
   padding: .2em 1em;
   margin-left: -2.5em;
}

.mess {
   height: 300px;
   display: table;
   width: 100%;
   margin: 0;
   padding: 0;
}

.mess-part {
   display: table-cell;
   height: 100%;
}

.mess-a { background-color: #452B33; }
.mess-b { background-color: #693B3E; }
.mess-c { background-color: #9E514E; }
.mess-d { background-color: #403834; }
.mess-e { background-color: #A6B5A1; }
   

button:hover {
   cursor: pointer;
}