body { background: linear-gradient(54deg, var(--petrol-dark) 0%, var(--petrol-light) 100%); background-attachment: fixed;  }  .btn-gray-gradient-bg, .gray-gradient-card-bg { background: linear-gradient(54deg, var(--btn-01) 0%, var(--btn-02) 100%); }  .btn-gray-gradient-bg:hover, .gray-gradient-card-bg:hover { filter: brightness(1.1); }  .back-to-top-btn {  position: fixed; bottom: 30px; right: 30px; z-index: 99;  background-color: var(--secondary); color: var(--primary); width: 50px; height: 50px; display: flex; align-items: center; justify-content: center; border-radius: 50%; box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15); border: none;  opacity: 0; transform: scale(.8); visibility: hidden; pointer-events: none; transition: opacity .3s ease, transform .3s ease, visibility 0s linear .3s; }  .back-to-top-btn.is-visible { opacity: 1; transform: scale(1); visibility: visible; pointer-events: auto; transition: opacity .3s ease, transform .3s ease; }  .back-to-top-btn:hover { background-color: #f8f8f8; transform: translateY(-3px) scale(1.05); }  .back-to-top-btn:focus-visible { outline: 3px solid var(--primary, #fff); outline-offset: 4px; }