Why does the % width and height for a shadow element in the shadow root of another customer element not work?

Question

HTML:

<options-container>
  <options-panel panel-type=“login”></options-panel>
</options-container>

Parent custom element styles:

options-container {
  display: inline-flex;
  flex-direction: column;
  justify-content: flex-start;
  align-items: center;
  height: calc(100vh - 52px);
  height: calc(100vh - (45px + 0.3vw));
  min-height: max(calc(56.25vw - 52px), calc(100vh - 52px));
  min-height: max(calc(56.25vw - (45px + 0.3vw)), calc(100vh - (45px + 0.3vw)));
  position: fixed;
  top: 52px;
  top: calc(45px + 0.3vw);
  right: 0;
  z-index: 1;
  width: calc(300px + 3vw);
  -webkit-backface-visibility: hidden;
  -webkit-perspective: 1000;
  -webkit-transform-style: preserve-3d;
  -webkit-transition: width 0.5s ease-in-out;
  -moz-transition: width 0.5s ease-in-out;
  -o-transition: width 0.5s ease-in-out;
  transition: width 0.5s ease-in-out;
  will-change: width;
  pointer-events: none;
}

Child element (in the shadow root of the above element) styles:

:host {
  display: inline-flex;
  justify-content: flex-start;
  align-items: center;
  flex-direction: column;
  width: 90%;
  height: auto;
  max-height: 100vh;
  padding: 10px;
  min-height: 10vw;
  background-color: var(--white, white);
  border: 2px solid var(--light-gray, lightgray);
  border: 0.2vw solid var(--light-gray, lightgray);
  box-sizing: border-box;
  margin-top: 20px;
  border-radius: 10px;
  border-radius: calc(8px + 0.3vw);
  overflow: hidden;
  box-shadow: 0px 0px 10px 0px var(--shadow, black);
  box-shadow: 0px 0px calc(8px + 0.3vw) 0px var(--shadow, black);
  pointer-events: auto;
  animation: fly-down 1.5s ease-out;
  animation-play-state: running;
  -webkit-transform: translate3d(0, 0, 0) !important;
  -webkit-backface-visibility: hidden;
  -webkit-transform-style: preserve-3d;
  -webkit-transition: max-height 0.5s ease-in-out 0.5s;
  -moz-transition: max-height 0.5s ease-in-out 0.5s;
  -o-transition: max-height 0.5s ease-in-out 0.5s;
  transition: max-height 0.5s ease-in-out 0.5s;
  will-change: max-height;
}

Parent Element Box Model

Child Element Box Model

Having real trouble trying to explain this behaviour, and more trouble trying to get the child element to become visible. I may be missing something really small, I don't know. But any guidance and/or explanation would be greatly appreciated!

Answer 1

Answer found!

Embarrassing, rookie error, I had attached a shadow root to the <options-container> element, which is why the child elements were not being rendered. Nothing to do with the CSS at all.

Note to self and others in a similar situation: Check the shadow root.

Doing

this.shadowroot = this.attachShadow({mode: 'open'});

was the answer.