html+css+js模拟select+option下拉菜单

以下是一个简单的html+css+js模拟select+option下拉菜单的示例：

HTML代码：

<div class="custom-select-wrapper">
  <div class="custom-select">
    <div class="custom-select__trigger">Select an option</div>
    <div class="custom-options">
      <span class="custom-option selected" data-value="1">Option 1</span>
      <span class="custom-option" data-value="2">Option 2</span>
      <span class="custom-option" data-value="3">Option 3</span>
      <span class="custom-option" data-value="4">Option 4</span>
      <span class="custom-option" data-value="5">Option 5</span>
    </div>
  </div>
</div>

CSS代码：

.custom-select-wrapper {
  position: relative;
  user-select: none;
  /* Prevents the select options from being selected */
}

.custom-select {
  position: relative;
  display: inline-block;
  cursor: pointer;
}

.custom-select__trigger {
  position: relative;
  display: block;
  width: 100%;
  padding: 0.5rem;
  font-size: 1rem;
  font-weight: 300;
  color: #fff;
  line-height: 1;
  background-color: #7b7b7b;
  border-radius: 0;
  transition: all 0.25s ease;
}

.custom-select__trigger:hover {
  background-color: #666;
}

.custom-select__trigger:after {
  position: absolute;
  display: block;
  content: "";
  top: 50%;
  right: 1rem;
  width: 0.5rem;
  height: 0.5rem;
  margin-top: -0.15rem;
  border-bottom: solid 0.2rem #fff;
  border-right: solid 0.2rem #fff;
  transform: rotate(45deg);
  transition: all 0.25s ease;
  transform-origin: 50% 50%;
}

.custom-select.open .custom-select__trigger:after {
  margin-top: -0.35rem;
  transform: rotate(-135deg);
}

.custom-options {
  position: absolute;
  display: none;
  top: 100%;
  left: 0;
  right: 0;
  z-index: 999;
  margin: 0;
  padding: 0;
  list-style: none;
  background-color: #fff;
  border: 1px solid #7b7b7b;
  border-top: none;
  border-radius: 0 0 4px 4px;
  box-shadow: 0 2px 2px rgba(0, 0, 0, 0.1);
}

.custom-options:before {
  position: absolute;
  display: block;
  content: "";
  top: -0.5rem;
  left: 50%;
  width: 1rem;
  height: 1rem;
  margin-left: -0.5rem;
  background-color: #fff;
  border-top: 1px solid #7b7b7b;
  border-left: 1px solid #7b7b7b;
  transform: rotate(45deg);
  z-index: -1;
}

.custom-option {
  position: relative;
  display: block;
  padding: 0.5rem;
  font-size: 1rem;
  font-weight: 300;
  color: #7b7b7b;
  line-height: 1;
  transition: all 0.25s ease;
  cursor: pointer;
}

.custom-option:hover,
.custom-option:focus {
  background-color: #f9f9f9;
}

.custom-option.selected {
  color: #fff;
  background-color: #7b7b7b;
}

.custom-select.open .custom-options {
  display: block;
}

JS代码：

const customSelects = document.querySelectorAll(".custom-select");

customSelects.forEach((customSelect) => {
  const customSelectTrigger = customSelect.querySelector(".custom-select__trigger");
  const customOptions = customSelect.querySelector(".custom-options");
  const customOptionList = customSelect.querySelectorAll(".custom-option");

  customSelectTrigger.addEventListener("click", () => {
    customSelect.classList.toggle("open");
  });

  customOptionList.forEach((customOption) => {
    customOption.addEventListener("click", () => {
      if (!customOption.classList.contains("selected")) {
        const selectedOption = customSelect.querySelector(".custom-option.selected");
        selectedOption.classList.remove("selected");
        customOption.classList.add("selected");
        customSelectTrigger.textContent = customOption.textContent;
      }
      customSelect.classList.remove("open");
    });
  });

  window.addEventListener("click", (e) => {
    if (!customSelect.contains(e.target)) {
      customSelect.classList.remove("open");
    }
  });
});

注意：此示例只是一个简单的模拟，实际使用时需要根据具体的需求进行相应的修改和优化。