#back-chip{
    position:fixed; left:24px; top:20px; z-index:700;
    font-weight:700; font-size:17px; letter-spacing:0.04em;
    color:var(--accent); background:var(--bg);
    padding:10px 16px; text-decoration:none;
    box-shadow:0 4px 24px rgba(0,0,0,0.12);
    opacity:0; pointer-events:none; transform:translateY(-8px);
    transition:opacity 0.25s ease-out, transform 0.25s ease-out,
               background 0.19s ease-out, color 0.19s ease-out;
  }
  #back-chip.on{ opacity:1; pointer-events:auto; transform:none; }
  #back-chip:hover{ background:var(--accent); color:var(--bg); }
  @media (max-width:720px){
    #back-chip{ left:14px; top:12px; }
  }