為什么對單個矩形設置animation-delay屬性時要寫成.spinner .line2{animation-delay: -1.1s;}而不能寫成.line2{animation-delay: -1.1s;}p.s.html部分如下：<div class="spinner">?<div class="line1"></div>?<div class="line2"></div>?<div class="line3"></div>?<div class="line4"></div>?<div class="line5"></div></div>