css大屏设置中间元素四周渐变透明效果
四周透明效果：
js
// 设置蒙版上下左右渐变显示
mask-image: linear-gradient(to right, rgba(0, 0, 0, 0) 0%, rgba(0, 0, 0, 1) 10%, rgba(0, 0, 0, 1) 90%, rgba(0, 0, 0, 0) 100%),
linear-gradient(to bottom, rgba(0, 0, 0, 0) 0%, rgba(0, 0, 0, 1) 10%, rgba(0, 0, 0, 1) 90%, rgba(0, 0, 0, 0) 100%);
mask-composite: intersect;