style.css

body {
  margin: 0;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
  color: #333;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

label {
  cursor: pointer;
}

main, header {
  display: flex;
  justify-content: space-between;
  width: 800px;
  max-width: 90%;
  margin: 0 auto;
  flex-wrap: wrap;
}

main {
  margin-bottom: 25px;
}

h1 {
  margin: 30px 0 40px;
  font-size: 2.5em;
  font-weight: 900;
}

.column {
  width: 48%;
}

@media screen and (max-width: 670px) {
  .column {
    width: 100%;
  }
}

.field-group {
  display: flex;
  align-items: center;
  margin: 0 0 20px;
}

.field-group--optional {
  display: block;
}

.field-group label {
  display: inline-block;
  margin: 0 10px 0 0;
}

#value-toggle:not(:checked) ~ .field-group {
  display: none;
}

.output-code {
  margin: 15px 0;
  min-height: 100px;
  background: #f7f7f7;
  color: #222;
  overflow: auto;
  border-radius: 3px;
}

.field-group input[type="number"] {
  border: 1px solid #888;
  border-radius: 3px;
  padding: 3px 7px;
}

.field-group input[type="color"] {
  -webkit-appearance: none;
  border: none;
  padding: 0;
  height: 30px;
  width: 28px;
  background: transparent;
  outline: none;
  cursor: pointer;
}

.field-group input[type="radio"] {
  margin: 0;
}

.output {
  display: flex;
  justify-content: center;
  align-items: center;
  margin: 0 0 40px;
}

.footer-text {
  margin: 0;
  padding: 30px 0;
  text-align: center;
  border-top: 1px solid #ccc;
  font-size: .8em;
}

.copy-btn {
  width: 156px;
  height: 40px;
  border: none;
  border-radius: 3px;
  margin: 0;
  padding: 12px 26px;
  color: #fff;
  background-color: #377cf0;
  cursor: pointer;
}

.copy-btn:hover {
  background-color: #1951b0;
}