body {
    background-color: lightgreen;
}

#post-div {
    display: flex; margin: auto;
}

#post-input {
    width: 500px;
}

#post-button {
    width: 150px;
    font-size: 14px;
}

#postlist-div {
    display: flex;
    margin: auto;
    margin-top: 2.5%;
}