// HTML代码
<div ref="dragArea" class="drag-area">
      <el-tooltip effect="dark" content="返回" placement="top">
        <el-button size="mini" icon="el-icon-back" circle @click="callback"></el-button>
      </el-tooltip>
    </div>

// JS代码
  mounted() {
    /**
   * 监听悬浮拖拽区域
   */
    this.$nextTick(() => {
      // 获取DOM元素
      let dragArea = this.$refs.dragArea;
      // 缓存 clientX clientY 的对象: 用于判断是点击事件还是移动事件
      let clientOffset = {};
      // 绑定鼠标按下事件
      dragArea.addEventListener("mousedown", (event) => {
        let offsetX = dragArea.getBoundingClientRect().left; // 获取当前的x轴距离
        let offsetY = dragArea.getBoundingClientRect().top; // 获取当前的y轴距离
        let innerX = event.clientX - offsetX; // 获取鼠标在方块内的x轴距
        let innerY = event.clientY - offsetY; // 获取鼠标在方块内的y轴距
        console.log(offsetX, offsetY, innerX, innerY);
        // 缓存 clientX clientY
        clientOffset.clientX = event.clientX;
        clientOffset.clientY = event.clientY;
        // 鼠标移动的时候不停的修改div的left和top值
        document.onmousemove = function (event) {
          dragArea.style.left = event.clientX - innerX + "px";
          dragArea.style.top = event.clientY - innerY + "px";
          // dragArea 距离顶部的距离
          let dragAreaTop = window.innerHeight - dragArea.getBoundingClientRect().height;
          // dragArea 距离左部的距离
          let dragAreaLeft = window.innerWidth - dragArea.getBoundingClientRect().width;
          // 边界判断处理
          // 1、设置左右不能动
          // dragArea.style.left = dragAreaLeft + "px";

          // 1.设置左侧边界
          if (dragArea.getBoundingClientRect().left <= 0) {
            dragArea.style.left = "0px";
          }
          // 2.设置右侧边界
          if (dragArea.getBoundingClientRect().left >= dragAreaLeft) {
            dragArea.style.left = dragAreaLeft + "px";
          }
          // 3、设置顶部边界
          if (dragArea.getBoundingClientRect().top <= 0) {
            dragArea.style.top = "0px";
          }
          // 4、设置底部边界
          if (dragArea.getBoundingClientRect().top >= dragAreaTop) {
            dragArea.style.top = dragAreaTop + "px";
          }
        };
        // 鼠标抬起时，清除绑定在文档上的mousemove和mouseup事件；否则鼠标抬起后还可以继续拖拽方块
        document.onmouseup = function () {
          document.onmousemove = null;
          document.onmouseup = null;
        };
      }, false);
      // 绑定鼠标松开事件
      dragArea.addEventListener('mouseup', (event) => {
        let clientX = event.clientX;
        let clientY = event.clientY;
        if (clientX === clientOffset.clientX && clientY === clientOffset.clientY) {
          console.log('click 事件');
        } else {
          console.log('drag 事件');
        }
      })
    });
  },

// css代码
<style scoped lang="scss">
.drag-area {
  position: fixed;
  right: 20px;
  top: 20%;
  z-index: 99999;
  padding: 13px;
  width: fit-content;
  opacity: 1;
  background-color: rgba(255, 255, 255, 0.1);
  border-radius: 8px;
  box-shadow: 0px 2px 15px 0px rgba(9, 41, 77, 0.15);
  cursor: move;
  user-select: none;
  text-align: center;
}
<style>

可拖拽悬浮按钮