如何更改输入按钮(正方形)的默认外观，使其看起来像三个垂直线？

input[type="button"] {
  border: none;
  width: 20px;
  height: 20px;
}

input[type="button"]::before,
input[type="button"]::after {
  content: "";
  display: block;
  width: 2px;
  height: 6px;
  background-color: #000;
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
}

input[type="button"]::before {
  top: 2px;
}

input[type="button"]::after {
  top: 12px;
}

.button-container {
  position: relative;
}

input[type="button"] {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}