You have to use absolute position for the second-level menu.
Try adding these.
nav ul#navul li {
transition: all .15s ease-in-out;
display: inline;
float: left;
border-bottom: 2px solid #8d0000;
position: relative;
}
.secondlvl {
position: absolute;
top: 38px;
left: -40px;
width: 145px;
}