1
#header{
margin: 0px;
padding: 0px;
border: 0px;
width:100%;
height:100px;
background-color:#00F;
}
#conteudo{
widows: 100%;
margin: 0px;
padding: 0px;
border: 0px;
height:500px;
background-color:#0F0;
}
#footer{
widows: 100%;
padding: 0px;
border: 0px;
margin: 0px;
height:100px;
background-color:#C3C;
}
#Conteudo-Top{
widows: 100%;
margin: 0px;
padding: 0px;
border: 0px;
height:250px;
background-color:red;
}
#Conteudo-Down{
margin: 0px;
padding: 0px;
border: 0px;
widows: 100%;
height:250px;
background-color:blueviolet;
}
<div id="site">
<div id="header"><h1>Header</h1></div>
<div id="conteudo">
<div id="Conteudo-Top"><h1>Conteudo TOP</h1></div>
<div id="Conteudo-Down"><h1>Conteudo Down</h1></div>
<div id="footer"><h1>Footer</h1></div>
</div>
Why - I believe it has something to do with the font size of the document. Use the universal selector by applying font-size:0; the spaces will disappear
– user60252