style.css

@import url('https://fonts.googleapis.com/css2?family=Space+Mono:wght@700&display=swap');

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Space Mono', monospace;
}

body {
  background-color: #c5e4e7;
}

.container {
  width: 100%;
  max-width: 600px;
  margin: 0 auto;
}

.logo {
  display: block;
  margin: 3rem auto;
}

main {
  background-color: #fff;
  padding: 1.5rem;
  border-radius: 20px 20px 0 0;
  min-height: 100vh;
}

h2 {
  text-transform: capitalize;
  font-size: 1rem;
  margin-bottom: 5px;
  color:hsl(184, 14%, 56%);
  margin-top: 1rem;
}

/* .input-field,
.select-tip-field {
  margin-bottom: 1.5rem;
} */

.input-field {
  background-color: hsl(189, 41%, 97%);
  display: flex;
  align-items: center;
  padding: .5rem 1rem;
  border-radius: 10px;
  font-size: 24px;
}

.input-field span,
.input-field input {
  border: 0;
  background-color: transparent;
  color: hsl(184, 14%, 56%);
}

.input-field input {
  text-align: end;
  width: 100%;
  font-size: 24px;
  color: hsl(183, 100%, 15%);
}

.input-field input:focus {
  outline: 0;
  border: 0;
}

.select-tip-field {
  display: grid;
  grid-template-columns: 49% 49%;
  justify-content: space-between;
}

.select-tip-field button {
  padding: .5rem 1rem;
  font-size: 1.1rem;
  border-radius: 5px;
  border: 0;
  background-color: hsl(183, 100%, 15%);
  color: #fff;
  font-weight: bold;
  cursor: pointer;
  margin-bottom: 10px;
}

#custom {
  background-color: hsl(189, 41%, 97%);
  color: hsl(184, 14%, 56%);
  text-transform: capitalize;
  text-align: end;
  font-size: 1rem;
  border: 0;
  border-radius: 5px;
  margin-bottom: 10px;
  padding: 0 1rem;
}

.display-field {
  background-color: hsl(183, 100%, 15%);
  color: #fff;
  border-radius: 10px;
  padding: 1.5rem;
  margin-top: 2rem;
}

.display-field > div {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 20px;
}

.display-field h2 {
  color: #fff;
  width: 100px;
  line-height: 1.3;
}

.display-field h2 span {
  color:  hsl(184, 14%, 56%);
  font-size: .8rem;
  display: block;
  text-transform: lowercase;
}

.display-figure {
  font-size: 2rem;
  color: hsl(172, 67%, 45%);
}

.display-field button {
  width: 100%;
  text-transform: uppercase;
  font-size: 1rem;
  padding: 10px;
  color: hsl(183, 100%, 15%);
  background-color: hsl(183, 98%, 20%);
  border: 0;
  border-radius: 5px;
  font-weight: 700;
  cursor: pointer;
}

.error-message {
  color: red;
  font-size: .7rem;
}