Вот так?
<!DOCTYPE html>
<html>
<head>
<title>Три Блока</title>
<link rel = "stylesheet" type = "text/css" href = "test.css">
</head>
<body>
<div class = "test_block block_1">
Блок 1
<div class = "test_block block_2">
Блок 2
<div class = "test_block block_3">
Блок 3
</div>
</div>
</div>
</body>
</html>
test.css:
.test_block {
width: 600px;
height: 200px;
font-size: 170px;
background-color: blue;
text-align: center;
}
.block_1:hover .block_2 {
display: block;
}
.block_2 {
display: none;
}
.block_2:hover .block_3 {
display: block;
}
.block_3 {
display: none;
}
