#back-to-top,
.top-bar {
    background: #222;
    color: #fff
}

body.dark,
body.dark .top-bar {
    background: #111
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box
}

.top-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 10px 20px;
    font-family: Arial, sans-serif;
    position: sticky;
    top: 0;
    z-index: 1000
}

#date-time {
    font-size: 14px
}

#back-to-top,
#theme-toggle {
    border: none;
    font-size: 18px;
    cursor: pointer
}

#theme-toggle {
    background: 0 0;
    color: inherit
}

#back-to-top {
    position: fixed;
    bottom: 20px;
    right: 20px;
    border-radius: 50%;
    padding: 12px 15px;
    display: none;
    box-shadow: 0 4px 6px rgba(0, 0, 0, .2);
    transition: opacity .3s
}

#back-to-top:hover {
    background: #444
}

body.dark {
    color: #eee
}

body.dark #back-to-top {
    background: #555
}