写个圣诞树，送给女朋友，使用前端html，css，JavaScript写

好的，这是一个使用 HTML、CSS 和 JavaScript 写的圣诞树的示例：

HTML:

<div id="christmas-tree">
  <div class="star"></div>
  <div class="trunk"></div>
  <div class="tree-section">
    <div class="tree-layer"></div>
    <div class="tree-layer"></div>
    <div class="tree-layer"></div>
    <div class="tree-layer"></div>
    <div class="tree-layer"></div>
  </div>
  <div class="gifts">
    <div class="gift"></div>
    <div class="gift"></div>
    <div class="gift"></div>
    <div class="gift"></div>
  </div>
</div>

CSS:

#christmas-tree {
  position: relative;
  width: 400px;
  height: 600px;
  margin: 0 auto;
}

.star {
  position: absolute;
  top: -30px;
  left: 50%;
  transform: translateX(-50%);
  width: 60px;
  height: 60px;
  border-radius: 50%;
  background: gold;
  box-shadow: 0 0 20px gold;
}

.trunk {
  position: absolute;
  bottom: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 40px;
  height: 80px;
  background: brown;
}

.tree-section {
  position: absolute;
  top: 50px;
  left: 50%;
  transform: translateX(-50%);
  width: 200px;
  height: 400px;
}

.tree-layer {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  border-radius: 50%;
  background: green;
  box-shadow: 0 0 20px green;
  transform: translateY(-50%);
}

.tree-layer:nth-child(1) {
  width: 200px;
  height: 200px;
}

.tree-layer:nth-child(2) {
  width: 180px;
  height: 180px;
  top: 20px;
}

.tree-layer:nth-child(3) {
  width: 160px;
  height: 160px;
  top: 40px;
}

.tree-layer:nth-child(4) {
  width: 140px;
  height: 140px;
  top: 60px;
}

.tree-layer:nth-child(5) {
  width: 120px;
  height: 120px;
  top: 80px;
}

.gifts {
  position: absolute;
  bottom: 60px;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
}

.gift {
  width: 50px;
  height: 50px;
  background