正如 Armedin 所說，您的 div 中沒有任何內(nèi)容。Width并且height 100%不會做任何事情。
我建議你不要把圖像作為背景，因為它不會改變 div 的尺寸。使用img標簽和display: inline;卡片 div。
.card {
width: 100%;
height: 100%;
background-size: cover;
display:inline;
}
<div class="poker is2d">
<div class="middle">
<div class="card two hearts"> <img src='data:image/svg+xml;base64,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'/></div>
<div class="card two hearts"> <img src='data:image/svg+xml;base64,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'/></div>
<div class="card two hearts"></div>
<div class="card"></div>
<div class="card"></div>
</div>
</div>
編輯：如果您不想使用img，可以將 img 設(shè)置為不可見，然后使用背景圖像，因為 div 內(nèi)部仍然有 img 標簽的尺寸。不是一個好的解決方案，但它會起作用。
