Problem CSS web background [closed]

Why do I get between the first and second element of my web (div) without the blank space if I have a transparent background or a white background?

I leave my website: link

I leave you my CSS code:

*{
    margin-top:  4px;
    margin-bottom: 4px;
}


#todo{
    width: 750px;
    height: 100px;
    font-family: "Times New Roman";
    font-size: 14;
    margin: auto;
    background: transparent; //esto tendría que hacer efecto...
}


div{
    background-color: #00FFFF;
}


img{
    float: left;
    width: 96px;
    height: 60px;

}


.columna{
    float: left;
    width: 280px;
    padding-left: 5px;
}


.descripcion{
    clear: left;
}