Good day everyone. I'm a novice with css and I'm trying to float two div tags within one div tag but I'm getting the following

I gave the parent div tag a light grey background so I know something is wrong somewhere as the background has disappeared just after I floated the div tags.
Here's my css below.
.menu.container {
    width: 100%;
    background-color: #F0F0F0;
}
.category {
    float: left;
}
Thanks a lot for your help!
 
     
    