/* 返回顶部按钮样式 */
#btn_backToTop { position: fixed; bottom: 24px; right: 24px; border: 0; background-color: #3B82F6; color: white; width: 48px; height: 48px; border-radius: 50%; display: flex; align-items: center; justify-content: center; box-shadow: 0 4px 6px rgba(0,0,0,0.1); opacity: 0; visibility: hidden; transition: opacity 0.3s ease, visibility 0.3s ease, background-color 0.3s ease; cursor: pointer; font-size: 1.25rem; z-index: 100; }
#btn_backToTop:hover { background-color: #2563EB; transform: scale(1.2);  }
#btn_backToTop.show { opacity: 1; visibility: visible; }
#btn_backToTop i { margin-right:0;}