main {
    margin: 32px;
    padding: 4px;
    border: 4px solid #000;
    border-radius: 16px;
    background: #fff8;
}

h1::before {
    content: "# ";
}
h2::before {
    content: "## ";
}
h3::before {
    content: "### ";
}

p {
    margin: 12px 0;
}

button {
    font: smaller TerminusTTF;
    margin: -4px 0;
    padding: 0px;
    border: 2px solid #fff;
    border-radius: 4px;
    background: #fff;
    color: #000;
}
button:hover {
    cursor: pointer;
    animation: pastel_rainbow_background 2s infinite linear;
}

:popover-open {
  position: fixed;
  margin: auto;
  width: 66%;
  min-width: min(480px, calc(100% - 32px));
  overflow-x: hidden;
  max-height: 66%;
  border: 4px solid #000;
  border-radius: 16px;
  filter: drop-shadow(0 0 16px #000);
  background: #fff;
  padding: 6px;
}
:popover-open img {
    max-width: 100%;
}
:popover-open > button.popover_close {
    display: block;
    position: relative;
    top: -6px;
    left: -6px;
    width: calc(100% + 12px);
    border: 0;
    border-radius: 0;
    border-bottom: 4px solid #000;
    margin: 0;
    background: #f00;
    color: #000;
    font-weight: bold;
    animation: none;
}