body {
  font-family: sans-serif;
  font-size: 13px;
  margin: 0;
  padding: 0;
}
#keyboard {
  width: 560px;
  margin: 10px auto;
  background: #aaa;
  border-radius: 3px;
}
#keyboard .row {
  box-sizing: border-box;
  height: 40px;
  display: flex;
}
#keyboard .row > div {
  background: #333;
  position: relative;
  border-radius: 3px;
  box-sizing: border-box;
  margin: 3px;
  font-family: sans-serif;
  text-align: center;
  font-weight: 100;
}
#keyboard .row > div.pressed {
  background: #ddd;
}
#keyboard .row > div .name {
  position: absolute;
  font-size: 8px;
  bottom: 3px;
  left: 3px;
  color: #ccc;
}
#keyboard .row > div .label {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  font-size: 14px;
  font-weight: 100;
  color: #eee;
}
#keyboard .row:first-child {
  height: 24px;
}
#keyboard .row:first-child > div {
  font-size: 12px;
  padding-top: 2.4px;
}
#piano {
  margin: 10px;
  font-size: 8px;
  position: relative;
  height: 150px;
  display: flex;
}
#piano .white {
  position: relative;
  box-sizing: border-box;
  flex-grow: 1;
  border: 1px solid #ccc;
  border-bottom-left-radius: 3px;
  border-bottom-right-radius: 3px;
}
#piano .white.current {
  background: #ffa;
}
#piano .label {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  text-align: center;
}
#piano .blacks-container {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  display: flex;
  justify-content: space-around;
  z-index: 1;
}
#piano .blacks-container > .black {
  position: relative;
  box-sizing: border-box;
  flex-grow: 0;
  background-color: black;
  border-bottom-left-radius: 3px;
  border-bottom-right-radius: 3px;
  margin-bottom: 52.5px;
}
#piano .blacks-container > .black.current {
  background: #ffa;
  border: 1px solid black;
}
#piano .blacks-container > .black .label {
  color: white;
}
#explanation {
  margin-top: 10px;
  padding: 20px;
  background: #333;
  color: #eee;
}
#explanation article {
  font-weight: 100;
  max-width: 600px;
  margin: auto;
}
#explanation article h2 {
  font-size: 2em;
  font-weight: normal;
  padding: 0;
  margin: 0 1em;
}
#explanation article a {
  color: #ccc;
  text-decoration: underline;
}
#explanation article a:visited {
  color: #aaa;
}