Not a perfect example, but you are best off removing your use of floating and replacing with a display led approach.
Something along these lines:
@media only screen and (min-width: 900px) {
nav > a, .dropNav, nav > div {
display: inline;
position: relative;
}
.dropList {
left: 0;
right: 0;
display: none;
position: absolute;
background-color: #f9f9f9;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
z-index: 1;
padding-left: 0;
}
}
solved Postioning of a clickable dropdown menu [closed]