di●▂●v响应式高宽比全自动添充剩下高宽比

<div class="outer">
    <div class="A"> 头顶部DIV </div>
    <div class="B">下边DIV </div>
</div>

html,
body { height: 100%; padding: 0; margin: 0; }
.outer { height: 100%; padding: 100px 0 0; box-sizing: border-box ; position: relative; }
.A { height: 100px; background: #BBE8F2; position: absolute; top: 0 ; left: 0 ; width: 100%; }
.B { height: 100%; background: #D9C666; }

<div class="outer">
    <div class="A">头顶部DIV</div>
    <div class="B">下边DIV</div>
</div>

html,
body { height: 100%; padding: 0; margin: 0; }
.outer { height: 100%; padding: 100px 0 0; box-sizing: border-box ; }
.A { height: 100px; margin: -100px 0 0; background: #BBE8F2; }
.B { height: 100%; background: #D9C666; }