style.css

/* http://meyerweb.com/eric/tools/css/reset/
   v2.0 | 20110126
   License: none (public domain)
*/
* { box-sizing: border-box }
html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, img, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
b, u, i, center,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead, tr, th, td,
article, aside, canvas, details, embed,
figure, figcaption, footer, header, hgroup,
menu, nav, output, ruby, section, summary,
time, mark, audio, video {
  margin: 0;
  padding: 0;
  border: 0;
  font-size: 100%;
  font: inherit;
  vertical-align: baseline;
}
/* HTML5 display-role reset for older browsers */
article, aside, details, figcaption, figure,
footer, header, hgroup, menu, nav, section {
  display: block;
}
body {
  line-height: 1;
  padding-bottom: 50px;
}
ol, ul {
  list-style: none;
}
blockquote, q {
  quotes: none;
}
blockquote:before, blockquote:after,
q:before, q:after {
  content: '';
  content: none;
}
table {
  border-collapse: collapse;
  border-spacing: 0;
}

div.styling {
  font-size: 20px;
}

div.centered {
  text-align: center;
  font-weight: bolder;
  padding: 15px 30px;
  margin: 5px auto;
  border: 1px solid black;
}

div.answer {
  display: flex;
  flex-wrap: wrap;
}
div.answer button {
  padding: 4px;
  border: 1px solid black;
  margin: 2px;
  flex-grow: 1;
  display: inline-block;
  min-width: 60px;
  font-size: 20px;
  font-weight: bold;
  width: calc(100% * (1/5) - 7px - 7px);
}

.title {
  font-size: 30px;
  text-align: center;
  padding: 5px;
  margin: 5px;
}
button {
  border: 1px solid;
  padding: 15px 30px;
  margin: 5px;
}

div.styling {
  display: flex;
}

div.result {
  margin-top: auto;
  margin-bottom: auto;
  margin-left: 5px;
  font-size: 20px;
  padding: 20px 20px;
  border-radius: 50%;
  width: 20px;
  height: 20px;
  text-align: center;
  background-color: white;
  border: 5px solid black;
}

div.result:before {
  position: relative;
  top: -10px;
  left: -6px;
  margin-bottom: 25px;
  content: "?";
}

div.correct {
  border: 5px solid darkgreen;
  background: green;
  content: "✔";
}
div.result.correct:before {
  content: "✔";
}
div.incorrect {
  border: 5px solid darkred;
  background: red;
}
div.result.incorrect:before {
  content: "✖";
}

div.score {
  padding: 5px;
  font-size: 30px;
  text-align: center;
  margin-right: auto;
  margin-top: auto;
  margin-bottom: auto;
}

div.input-bar {
  margin: auto;
  border: 1px solid black;
  flex-grow: 1;
  padding: 2px 2px;
  margin: 5px;
}
div.input-block {
  flex: 1;
  display: inline-table;
  border: 1px solid black;
  background: #a0a0a0;
  padding: 5px;
  margin: auto 2px auto auto;
  font-size: 24px;
  vertical-align: middle;
  align-items: center;
}
button.clear {
  margin-left: auto;
}

.dropdown {
  width: 50%;
  position: absolute;
  bottom: 0px;
  padding: 0px 0px;
  border: 1px solid black;
  background-color: white;
  position: fixed;
}
.dropdown.active .label:nth-child(1) {

}
.dropdown.active .label + .label {
  border-top: 1px solid black;
}
.dropdown.active .label:last-child:after {
  content: '⬆';
  float: right;
}

.dropdown .label.active:after {
  content: '⬇';
  float: right;
}
.dropdown.active .label {
  display: block;
  padding: 10px;
}

.dropdown .label {
  display: none;
}
.dropdown .label.active {
  display: block;
  padding: 10px;
}