.img-responsive {
    transition: opacity 0.3s ease-in-out;
    background-size: cover;
    background-position: center;
    position: relative;
}

/* 加载状态的动画 */
.img-responsive.loading::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 30px;
    height: 30px;
    margin: -15px 0 0 -15px;
    border: 2px solid rgba(0,0,0,0.1);
    border-top-color: #206bc4;
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

/* 加载错误状态 */
.img-responsive.error::after {
    content: '!';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 20px;
    color: #cd201f;
}

/* 加载完成的渐变效果 */
.img-responsive:not(.loaded) {
    opacity: 0.6;
}

.img-responsive.loaded {
    opacity: 1;
}

/* 旋转动画关键帧 */
@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* 图片容器的响应式比例 */
.img-responsive-3x1 {
    padding-top: 33.333%;
}

.img-responsive-1x1 {
    padding-top: 100%;
}