style.css

/* Reset */
html, body, h1, p {
  margin: 0;
  padding: 0;
}

* {
  box-sizing: border-box;
}

html, body {
  height: 100%;
}

html {
  font-family: Arial, sans-serif;
  color: #222;
  line-height: 1.5;
}

body {
  display: flex;
  flex-direction: column;
  padding: 5px 10px;
}

a {
  color: #3473ee;
}

.controls {
  display: flex;
  flex-direction: column;
  padding: 10px 0;
  align-self: center;
  width: 80vmin;
  height: 60vmin;
}

.controls .row {
  flex: 1;
  display: flex;
}

.controls button {
  flex: 1;
  color: #888;
  font-size: 10vmin;
  background: none;
  border: 2px solid;
  margin: 2px;
  border-radius: 7px;
  cursor: pointer;
}

.controls .dummy {
  visibility: hidden;
}

#max-score-grid {
  background: #8883;
}

#share {
  display: inline-block;
}

footer {
  margin-top: auto;
  font-size: 0.9rem;
}

.invisible {
  display: none !important;
}

.touch .no-touch-only,
.no-touch .touch-only {
  display: none;
}

/* Expandable "component". Uses the checkbox hack to expand and collapse their
   content without JS */
.expandable {
  overflow: hidden;
}

.expandable-checkbox {
  display: none;
}

.expandable-content,
.expand-toggle,
.collapse-toggle {
  transition: all .4s;
}

.expandable-content {
  position: relative;
  display: inline-block;
}

.expand-toggle {
  position: absolute;
  right: 0;
  top: 0;
  transform: translateX(100%);
}

.expand-toggle,
.collapse-toggle {
  font-weight: bold;
  cursor: pointer;
}

.help-toggle {
  color: #0bc3ff;;
}

.high-score-toggle {
  color: #ff8c0b;
}

.collapse-toggle {
  color: #aaa;
  opacity: 0;
}

.expandable-checkbox:not(:checked) ~ .expandable-content {
  transform: translateX(-100%);
}

.expandable-checkbox:checked ~ .expandable-content .collapse-toggle {
  opacity: 1;
}

.expandable-checkbox:checked ~ .expandable-content .expand-toggle {
  opacity: 0;
}

@media (max-width: 30em) {
  html {
    font-size: 1.3em;
  }
}

@media (prefers-color-scheme: dark) {
  html {
    background: #222;
    color: #eee;
  }
}

/* Icon font styles copied from Fontello. */
@font-face {
  font-family: 'icons';
  src: url('icons.woff2?40046441') format('woff2');
  font-weight: normal;
  font-style: normal;
}
[class^="icon-"]:before, [class*=" icon-"]:before {
  font-family: "icons";
  font-style: normal;
  font-weight: normal;
  speak: none;
  display: inline-block;
  text-decoration: inherit;
  width: 1em;
  margin-right: .2em;
  text-align: center;
  /* For safety - reset parent styles, that can break glyph codes*/
  font-variant: normal;
  text-transform: none;
  /* Animation center compensation - margins should be symmetric */
  /* remove if not needed */
  margin-left: .2em;
  /* Font smoothing. That was taken from TWBS */
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.icon-share:before { content: '\e811'; }