<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>ГГ</title>
<style>
div {
width: 100px;
height: 100px;
background-color: red;
}
.container {
width: 100%;
height: 300px;
background-color: transparent;
border: 1px solid green;
text-align: center;
}
.div1 {
float: left;
}
.div2 {
display: inline-block;
}
.div3 {
float: right;
}
</style>
</head>
<body>
<div class="container">
<div class="div1">первый</div>
<div class="div2">второй</div>
<div class="div3">третий</div>
</div>
</body>
</html>