style.css

@import url('https://fonts.googleapis.com/css2?family=Space+Mono:wght@400;700&display=swap');
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
:root {
  --strong-cyan: hsl(172, 67%, 45%);
  --very-dark-cyan: hsl(183, 100%, 15%);
  --dark-grayish-cyan: hsl(186, 14%, 43%);
  --grayish-cyan: hsl(184, 14%, 56%);
  --light-grayish-cyan: hsl(185, 41%, 84%);
  --very-light-grayish-cyan: hsl(189, 41%, 97%);
  --white: hsl(0, 0%, 100%);
  --font-size: 1.5rem;
}
body {
  font-family: 'space mono', 'sans serif';
  background: var(--light-grayish-cyan);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  gap: 1rem;
}
h1 {
  background: -webkit-linear-gradient(to right, var(--strong-cyan), #3c32cc);
  background: linear-gradient(to right, var(--strong-cyan), #3c32cc);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.container {
  background: var(--white);
  padding: 2rem 1.5rem;
  border-radius: 1rem;
  display: flex;
  width: min(93%, 50rem);
  gap: 1rem;
}
.calculator,
.results-container {
  flex: 1;
}
.calculator {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}
div {
  position: relative;
}

.icon {
  position: absolute;
  top: 50%;
  left: 0.2rem;
  stroke: var(--grayish-cyan);
}
input {
  outline: none;
  background: var(--very-light-grayish-cyan);
  border: none;
  border-radius: 0.2rem;
  color: var(--very-dark-cyan);
  text-align: right;
  font-family: inherit;
  width: 100%;
}
input:focus {
  outline: 3px solid var(--strong-cyan);
}
input:focus + .icon {
  stroke: var(--strong-cyan);
}
label {
  font-size: 1.1rem;
  color: var(--grayish-cyan);
  margin-bottom: 0.2rem;
}

input.standard.invalid {
  outline: 3px solid rgb(255, 81, 0);
}

.calculator input.standard {
  display: block;
  padding: 0.3rem;
  padding-left: 1.9rem;
  font-size: var(--font-size);
  font-weight: 700;
}
input.standard::placeholder {
  color: var(--grayish-cyan);
}
input[type='number']::-webkit-inner-spin-button {
  appearance: none;
}

.custom {
  font-size: 1.2em;
  padding: 0.2rem 0.4rem;
  font-size: var(--font-size);
  font-weight: 700;
}
.custom.active {
  outline: 3px solid var(--grayish-cyan);
}
.custom::placeholder {
  color: var(--very-dark-cyan);
  font-weight: 700;
}
.options {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.5rem;
}
.btn {
  background: var(--very-dark-cyan);
  color: var(--grayish-cyan);
  font-weight: 700;
  padding: 0.3rem 0.5rem;
  font-family: inherit;
  border-radius: 0.2rem;
  cursor: pointer;
  font-size: 1.3rem;
  outline: none;
  border: none;
  transition: 0.5s background-color, 0.5s color;
}

.btn:hover {
  background: var(--light-grayish-cyan);
  color: #000;
}
.btn.active {
  background: var(--strong-cyan);
  color: #000;
}
button:focus {
  outline: 4px solid var(--light-grayish-cyan);
}

.results-container {
  background: var(--very-dark-cyan);
  border-radius: 0.5rem;
  padding: 2rem 1rem 1rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.results-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
small {
  color: var(--grayish-cyan);
}
.results-item p {
  color: var(--light-grayish-cyan);
}
.results-item span {
  display: block;
  font-size: 2.2rem;
  color: var(--strong-cyan);
  font-weight: 700;
}
.reset {
  margin-top: auto;
  text-transform: uppercase;
  padding: 0.5rem 0.3rem;
  font-size: 1.1rem;
  border-radius: 0.2rem;
  outline: none;
  border: none;
  cursor: pointer;
  background: var(--strong-cyan);
  transition: 0.5s background-color, 0.5s color;
  font-family: inherit;
  font-weight: 700;
}
@media (min-width: 680px) {
  .reset:hover {
    background: var(--light-grayish-cyan);
  }
}

@media (max-width: 680px) {
  .container {
    flex-direction: column;
    gap: 1.3rem;
  }
  .calculator {
    gap: 1.7rem;
  }
}
@media (max-width: 420px) {
  .options {
    grid-template-columns: repeat(2, 1fr);
  }
}