/* 子页面：按原视频 720×1280 构图 1:1 还原，--u = 原视频 1 像素对应的屏幕像素 */
.stage{position:absolute;left:50%;top:50%;width:calc(var(--u)*720);height:calc(var(--u)*1280);
  -webkit-transform:translate(-50%,-50%);transform:translate(-50%,-50%);z-index:1}
.s{position:absolute;display:block}
.s-img{width:100%;height:auto}
.stage .anim{position:absolute}
.stage .frame{position:absolute}
.stage .frame-img{position:absolute;left:0;top:0;width:100%;height:100%}
.stage .field{position:absolute;z-index:2;border:0;outline:0;background:transparent;display:flex;align-items:center;justify-content:center;
  font-size:calc(var(--u)*21);font-weight:700;text-align:center;letter-spacing:calc(var(--u)*1);line-height:1;padding:0}
.stage .btn{position:absolute;border:0;background:transparent;padding:0;cursor:pointer;transition:transform .12s ease}
.stage .btn img{width:100%;height:auto;display:block}
.stage .btn:active,.stage .btn.pressed{-webkit-transform:scale(.92);transform:scale(.92)}
.nav{z-index:20}