* {
  box-sizing: border-box;
}


.menu {
   position: fixed;
   left: 0;
   bottom: 0;   
  width: 50%;
  padding: 2px;
  float: left;  
  border: 1px solid red;
  background-color:red;
}

.main {
position: fixed;
   right: 0;
   bottom: 0;
   padding: 2px;
  width: 50%;
  float: left;  
  border: 1px solid green;
  background-color:green;
}