You can use width:50%
, like this:
#one{
width:50%;
float:left;
height:100px;
}
#two{
width:50%;
float:left;
height:100px;
}
td, tr, table{
border:1px solid black; // visual
text-align:center; // text's also centered, if required
}
It is responsive also, so it readjusts on window resize.