body {
    margin: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

main {
    flex: 1 0 auto; /* fills remaining space between header and footer */
    display: flex;
    flex-direction: column;
    align-items: center;     /* horizontal centering */
    text-align: center;
}
.center-text {
    color: darkgreen;
    text-align:center;
    margin-top: 0px;
    padding: 0 10px;
}
footer {
    color: darkgreen;
    text-align: center;
    padding: 10px;
    width: 100%;
    flex-shrink: 0;
}