#centered-content{
position: absolute;
float: left;
max-width: 400px;
margin: 0;
left: 50%;
top: 50%;
transform: translate(-50%,-50%);
}
img{
position: relative;
float: left;
height: 2.5em;
left: 50%;
transform: translateX(-50%);
}
form{
position: relative;
float: left;
width: 100%;
} 
form button{
position: relative;
float: left;
left: 50%;
transform: translateX(-50%);
}