style.css

* {
  box-sizing: border-box;
}

body {
  font-family: Helvetica,Arial,sans-serif;
  font-size: 16px;
  line-height: 1.5em;
  margin: 0;
}
@media only screen and (max-width: 900px) {
  body {
    font-size: 14px;
  }
}

input {
  font: inherit;
  color: #000;
  padding: 0;
  margin: 0.5em 0;
  background-color: transparent;
  border: none;
  outline: none;
  width: 100%;
  border-bottom: 1px solid #757575;
}

button {
  background-color: #3e50b4;
  padding: 10px 30px;
  font-size: 16px;
  font-weight: bold;
  border: none;
  border-radius: 5px;
  color: white;
  box-shadow: 1px 1px 7px 1px rgba(0, 0, 0, 0.25);
}
button:hover {
  cursor: pointer;
}

.header {
  background-color: #3e50b4;
}
.header h1 {
  font-size: 45px;
  font-weight: 300;
  line-height: 48px;
}
.header h1,
.header p {
  color: white;
}
@media only screen and (max-width: 900px) {
  .header h1 {
    font-size: 22px;
    line-height: 25px;
  }
}

.content {
  width: 95%;
  max-width: 900px;
  padding: 40px;
}
@media only screen and (max-width: 900px) {
  .content {
    padding: 16px;
  }
}

#resultcontainer {
  border-radius: 10px;
  padding: 40px;
  -webkit-transition: background-color 0.6s ease;
  transition: background-color 0.6s ease;
}
#result {
  background-color: rgba(255, 255, 255, 0.5);
  border-radius: 10px;
  padding: 10px;
}