style.css

html,
body {
  background: rgb(18, 18, 18);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Ubuntu,
    "Helvetica Neue", sans-serif;
  color: #fff;
}

* {
  box-sizing: border-box;
}

h1,
h4 {
  color: rgb(248, 232, 28);
  text-align: center;
}

p {
  text-align: center;
  max-width: 600px;
  margin: 20px auto;
}

.wrapper {
  width: 80%;
  display: flex;
  margin: 0 auto;
  flex-direction: column;
}

.box {
  margin: 0 auto;
  width: 80%;
  max-width: 1200px;
}
#target {
  float: left;
}

#code-wrapper {
  float: right;
}

.box > * {
  /* flex: 1 1 0; */
  /* flex-basis: 100%; */
  width: calc(50% - 20px);
  padding: 10px;
  height: 100%;
  min-height: 350px;
}

@media (max-width: 700px) {
  .wrapper {
    width: 100%;
  }
  .box {
    flex-direction: column-reverse;
  }
  .box > * {
    width: 100%;
  }
}

form {
  margin: 0 auto;
  display: flex;
  width: 300px;
  border-radius: 5px;
  border: 1px solid #fff;
}

a {
  color: rgb(248, 232, 28);
}

form input {
  flex: 1;
  outline: none;
  border: 0;
  background: transparent;
  padding: 10px;
  color: #fff;
}

form button,
button {
  border: 0;
  border-left: 1px solid #fff;
  background: transparent;
  color: #fff;
  padding: 5px 20px;
  cursor: pointer;
}

#demo {
  margin: 0 auto;
  border: 1px solid #fff;
  border-radius: 5px;
  margin: 0 auto;
  display: block;
}

img {
  max-width: 100%;
}