style.css

@import url('https://fonts.googleapis.com/css2?family=Montserrat:ital,wght@0,100..900;1,100..900&display=swap');
*, *::after, *::before {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  font-size: 62.5%;
}

html, body {
  overflow-x: hidden;
}

:root {
  --color-primary: #007BFF;
  --color-primary-light: #2680D9;
}

body {
  font-size: 1.6rem;
  font-family: "Montserrat", sans-serif;
}

.header {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 2rem 1rem;
  background-color: var(--color-primary);
  gap: 1rem;
}

.header h1, .header p {
  color: #fff;
  text-align: center;
}

.header h1 {
  text-transform: capitalize;
  font-weight: 600;
}

.header p {
  font-weight: 500;
}

.input-form {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  margin-top: 5rem;
  gap: 3rem;
}

.user-input {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 2rem;
}

.user-input label {
  font-size: 4rem;
  text-transform: capitalize;
  font-weight: 500;
  text-align: center;
}

.user-input--input {
  padding: 2rem 3rem;
  font-size: 3rem;
  text-align: center;
  font-weight: 600;
}

.error {
  color: crimson;
  text-transform: uppercase;
  font-weight: 600;
}

@media screen and (max-width: 31.25em) {
  .input-form {
    width: 100vw;
  }

  .user-input label {
    width: 100%;
  }

  .user-input--input {
    width: 100%;
  }

  .output {
    width: 100vw;
  }
}

.convert-button {
  border: none;
  outline: none;
  font-size: 2rem;
  padding: 2rem 3rem;
  text-transform: uppercase;
  background-color: var(--color-primary);
  color: #fff;
  border-radius: 5px;
  cursor: pointer;
}

.output {
  text-align: center;
  margin-top: 3rem;
  font-size: 4rem;
}