body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    background: #f9f9f9;
}

.explanation,.transaction,.transaction_exp,#header,#main {
    background: #fff;
    padding: 2em 3em;
    margin-top: 2em;
    border-radius: 10px;
    box-shadow: 0 0 10px rgba(0,0,0,0.1);
}

form {
    margin: 1em 0;
}

textarea, button {
    margin-top: 0.5em;
}