#stb-btn{
    position:fixed;
    right:18px;
    bottom:18px;
    width:64px;
    height:64px;
    padding:0;
    border:none;
    border-radius:50%;
    background:#ff7a00;
    color:#ffffff;
    display:flex;
    align-items:center;
    justify-content:center;
    cursor:pointer;
    box-shadow:0 4px 12px rgba(0,0,0,.25);
    opacity:0;
    visibility:hidden;
    transform:scale(.8);
    transition:opacity .3s ease, transform .3s ease;
    z-index:9999;
}
#stb-btn.show{
    opacity:1;
    visibility:visible;
    transform:scale(1);
}
#stb-btn:hover{
    transform:scale(1.08);
}
/* SVG styles */
.stb-svg{
    width:64px;
    height:64px;
}
.track{
    fill:none;
    stroke:rgba(255,255,255,0.25);
    stroke-width:4;
    transform:rotate(-90deg);
    transform-origin:center;
}
.progress{
    fill:none;
    stroke:#ffffff;
    stroke-width:4;
    stroke-linecap:round;
    transform:rotate(-90deg);
    transform-origin:center;
    transition:stroke-dashoffset 0.15s linear;
}
.arrow{
    fill:none;
    stroke:#ffffff;
    stroke-width:4;
    stroke-linecap:round;
    stroke-linejoin:round;
    pointer-events:none;
}