/* 回到顶部按钮样式 */
.back-to-top {
    position: fixed;
    left: 20px;
    bottom: 20px;
    z-index: 1000;
    transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.back-to-top-btn {
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    border: none;
    box-shadow: 0 4px 15px rgba(102, 126, 234, 0.4);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    color: white;
    position: relative;
    overflow: hidden;
}

.back-to-top-btn::before {
    content: '';
    position: absolute;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
    background: linear-gradient(45deg, transparent, rgba(255, 255, 255, 0.2), transparent);
    transform: rotate(45deg);
    transition: left 0.7s;
    left: -100%;
}

.back-to-top-btn:hover {
    transform: scale(1.15) translateY(-5px);
    box-shadow: 0 8px 30px rgba(102, 126, 234, 0.6);
}

.back-to-top-btn:hover::before {
    left: 100%;
}

.back-to-top-btn:active {
    transform: scale(0.95);
    box-shadow: 0 2px 10px rgba(102, 126, 234, 0.3);
}

.back-to-top-btn svg {
    width: 24px;
    height: 24px;
    transition: all 0.3s ease;
    z-index: 1;
    position: relative;
}

.back-to-top-btn:hover svg {
    transform: translateY(-2px) rotate(360deg);
}

/* 隐藏状态（通过JS控制） */
.back-to-top.hidden {
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transform: translateY(20px) scale(0.8);
}

/* 显示状态 */
.back-to-top.visible {
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
    transform: translateY(0) scale(1);
}

/* 响应式设计 */
@media (max-width: 768px) {
    .back-to-top {
        left: 10px;
        bottom: 10px;
    }
    
    .back-to-top-btn {
        width: 45px;
        height: 45px;
    }
    
    .back-to-top-btn svg {
        width: 20px;
        height: 20px;
    }
}