为什么显示：flex在父级破坏CSS动画上？

Question

我正在使用Jonathan Suh的汉堡菜单。在我的项目中，当点击汉堡包时，我需要一个父容器作为flex容器。动画在没有显示弹性的情况下工作正常，但它会使用flex父级跳到完成状态。我无法弄清楚导致它跳过的原因。以下是我的代码，证明了这个问题。

.hamburger {
  padding: 15px 15px;
  display: inline-block;
  cursor: pointer;
  transition-property: opacity, filter;
  transition-duration: 0.15s;
  transition-timing-function: linear;
  font: inherit;
  color: inherit;
  text-transform: none;
  background-color: transparent;
  border: 0;
  margin: 0;
  overflow: visible;
}

.hamburger:hover {
  opacity: 0.7;
}

.hamburger-box {
  width: 40px;
  height: 24px;
  display: inline-block;
  position: relative;
}

.hamburger-inner {
  display: block;
  top: 50%;
  margin-top: -2px;
}

.hamburger-inner,
.hamburger-inner::before,
.hamburger-inner::after {
  width: 40px;
  height: 4px;
  background-color: #000;
  border-radius: 4px;
  position: absolute;
  transition-property: transform;
  transition-duration: 0.15s;
  transition-timing-function: ease;
}

.hamburger-inner::before,
.hamburger-inner::after {
  content: "";
  display: block;
}

.hamburger-inner::before {
  top: -10px;
}

.hamburger-inner::after {
  bottom: -10px;
}

.hamburger--collapse .hamburger-inner {
  top: auto;
  bottom: 0;
  transition-duration: 0.13s;
  transition-delay: 0.13s;
  transition-timing-function: cubic-bezier(0.55, 0.055, 0.675, 0.19);
}

.hamburger--collapse .hamburger-inner::after {
  top: -20px;
  transition: top 0.2s 0.2s cubic-bezier(0.33333, 0.66667, 0.66667, 1), opacity 0.1s linear;
}

.hamburger--collapse .hamburger-inner::before {
  transition: top 0.12s 0.2s cubic-bezier(0.33333, 0.66667, 0.66667, 1), transform 0.13s cubic-bezier(0.55, 0.055, 0.675, 0.19);
}

.hamburger--collapse.is-active .hamburger-inner {
  transform: translate3d(0, -10px, 0) rotate(-45deg);
  transition-delay: 0.22s;
  transition-timing-function: cubic-bezier(0.215, 0.61, 0.355, 1);
}

.hamburger--collapse.is-active .hamburger-inner::after {
  top: 0;
  opacity: 0;
  transition: top 0.2s cubic-bezier(0.33333, 0, 0.66667, 0.33333), opacity 0.1s 0.22s linear;
}

.hamburger--collapse.is-active .hamburger-inner::before {
  top: 0;
  transform: rotate(-90deg);
  transition: top 0.1s 0.16s cubic-bezier(0.33333, 0, 0.66667, 0.33333), transform 0.13s 0.25s cubic-bezier(0.215, 0.61, 0.355, 1);
}

.header--is-active {
  display: flex;
}

<div class="header">
  <button class="hamburger hamburger--collapse" type="button">
    <span class="hamburger-box">
      <span class="hamburger-inner"></span>
    </span>
  </button>
</div>

{{1}}