#main
{
    border: 1px solid black;
    width: 600px;
    height: 400px;
    position: relative;
}

.player
{
    width: 30px;
    height: 30px;
    position: absolute;
    top: 350px;
    background-color: blue;
    border-radius: 5px;
}

.bullet
{
    width: 10px;
    height: 10px;
    position: absolute;
    background-color: black;
    border-radius: 5px;
}

.alien
{
    border-bottom-left-radius: 15px;
    border-bottom-right-radius: 15px;
    width: 30px;
    height: 30px;
    position: absolute;
    background-color: red;
}

.aliengroup
{
    width: 400px;
    height: 150px;
    position: absolute;
}