/* ========== 底部导航 ========== */
        .bottom-nav {
          position: fixed;
          bottom: 0;
          left: 0;
          width: 100%;
          height: calc(var(--nav-height) + env(safe-area-inset-bottom)); 
          background: var(--nav-bg);
          display: flex;
          justify-content: space-around;
          align-items: flex-start; 
          padding-top: 12px; 
          border-top: none; 
          z-index: 100; 
          padding-bottom: env(safe-area-inset-bottom);
          transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1); 
        }

        .bottom-nav.nav-hidden {
          transform: translateY(100%);
        }

        .nav-item {
          flex: 1; display: flex; flex-direction: column; align-items: center; justify-content: center;
          color: var(--nav-icon-normal); height: 40px; transition: color 0.3s;
        }
        .nav-item.active { color: var(--nav-icon-active); }
        .nav-icon { margin-bottom: 4px; }
        .nav-label { font-family: var(--font-sans); font-size: 9px; letter-spacing: 1px; text-transform: uppercase; font-weight: 500;}