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HTML 

              
                    <div class="tip__calc">
      <div class="tip">
        <div class="calc__form--label">Tip Amount</div>
        <div class="calc__form--value">
          <sup>$</sup><span class="tip__total--amount value">12.00</span>
        </div>
      </div>
      <div class="tip">
        <div class="calc__form--label">Total per Person</div>
        <div class="calc__form--value">
          <sup>$</sup><span class="tip__pers--amount value">4.00</span>
        </div>
      </div>
      <form id="calc__form" class="calc__form" method="" action="">
        <div class="row calc__form--input">
          <div class="input">
            <input
              class=""
              name="total"
              type="number"
              placeholder=""
              min="0"
              step="0.01"
              value="60.00"
              size="8"
            />
            <label class="calc__form--label" for="total">Bill Amount</label>
          </div>
          <div class="input">
            <input
              class=""
              name="nb-people"
              type="number"
              placeholder=""
              min="1"
              step="1"
              value="3"
              size="4"
            />
            <label class="calc__form--label" for="total"
              >Number of People</label
            >
          </div>
        </div>
        <div class="row calc__form--radio">
          <div class="radio">
            <input type="radio" name="tip" id="5p" value="0.05" />
            <label class="form-control" for="5p">5%</label>
          </div>
          <div class="radio">
            <input type="radio" name="tip" id="10p" value="0.1" />
            <label class="form-control" for="10p">10%</label>
          </div>
          <div class="radio">
            <input type="radio" name="tip" id="15p" value="0.15" />
            <label class="form-control" for="15p">15%</label>
          </div>
          <div class="radio">
            <input type="radio" name="tip" id="20p" value="0.2" checked="checked" />
            <label class="form-control" for="20p">20%</label>
          </div>
        </div>
        <div class="row calc__form--submit">
          <button class="" name="submit" type="submit">Calculate</button>
        </div>
      </form>
    </div>
!

CSS 

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

:root {
  --background-color: #f6f6f3;
  --form-background-color: #f7f7f7;
  --tips-background-color: #eeeeee;
  --border-color: #dedede;
  --discount-color: #60c1b6;
  --button-color: #ed7861;
  --text-color: #333;
}

body {
  background-color: var(--background-color);
  font-family: "Inter", sans-serif;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 2rem;
  color: var(--text-color);
}

.tip__calc {
  background: #ffffff;
  box-shadow: 0px 0px 48px rgba(148, 146, 120, 0.23);
  border-radius: 22px;

  display: flex;
  flex-direction: column;
  align-items: center;

  padding-top: 1rem;
  max-width: 50rem;
}

.tip {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  width: 100%;
  padding: 1.5rem 0;
}

.tip + .tip {
  border-top: 1px solid var(--border-color);
}

.calc__form {
  background-color: var(--form-background-color);
  display: flex;
  flex-direction: column;
  border-radius: 1.5rem;
}

.calc__form--label {
  font-family: "Roboto Mono", monospace;
  font-size: 1rem;
  line-height: 1.25;
  padding: 1rem 2rem;
}

.calc__form--value {
  font-size: 5.5rem;
}

.calc__form--value sup {
  font-size: 3.25rem;
}

.calc__form--input {
  display: flex;
  flex-direction: column;
}

.calc__form--input .input {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 65px 45px 45px;
}

.calc__form--input .input:not(:last-child) {
  border-right: 1px solid var(--border-color);
}

input[type="number"] {
  border: none;
  border-bottom: 3.2px dotted var(--border-color);
  text-align: center;
  background-color: transparent;
  font-size: 4rem;
  line-height: 1;
  width: 100%;
}

[name="total"] {
  background: url("https://codepen.davidroessli.com/img/dollar.svg") left 15px no-repeat;
  padding-left: 40px;
}

[name="nb-people"] {
  background: url("https://codepen.davidroessli.com/img/people.svg") left 20px no-repeat;
  padding-left: 40px;
}

.calc__form--radio {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  gap: 1rem;
  align-items: center;
  justify-content: space-between;
  background-color: var(--tips-background-color);
  padding: 1.5rem 2rem;

  font-family: "Roboto Mono", monospace;
  font-size: 24px;
  font-weight: 700;
  line-height: 2rem;
  color: var(--discount-color);

  border: 1px solid var(--border-color);
  border-width: 1px 0;
}

.radio {
  display: grid;
}

.radio input {
  grid-area: 1 / 1 / 4 / 4;
}

.radio label {
  grid-area: 2 / 2 / 2 / 2;
  z-index: 2;
}

input[type="radio"] {
  -webkit-appearance: none;
  appearance: none;
  background-color: #fff;
  margin: 0;
  font: inherit;
  color: currentColor;
  width: 150px;
  height: 75px;
  border-radius: 18px;
  transform: translateY(-0.075em);

  display: grid;
  place-content: center;
}

input[type="radio"]::before {
  content: "";
  width: 150px;
  height: 75px;
  border-radius: 18px;
  transform: scale(0);
  transition: 120ms transform ease-in-out;
  box-shadow: inset 1em 1em var(--form-control-color);
}

input[type="radio"]:checked + label {
  color: white;
}

input[type="radio"]:checked::before {
  transform: scale(1);
  background-color: var(--discount-color);
}

input[type="radio"]:focus {
  outline: max(2px, 0.15em) solid currentColor;
  outline-offset: max(2px, 0.15em);
}

.calc__form--submit {
  display: flex;
  flex-direction: row;
  justify-content: flex-end;
  padding: 2rem;
}

[name="submit"] {
  font-family: "Roboto Mono", monospace;
  font-size: 24px;
  font-weight: 700;
  line-height: 2rem;
  text-align: center;
  letter-spacing: 0.15em;
  color: #ffffff;

  background-color: var(--button-color);
  padding: 18px 75px;
  box-shadow: 0px 1.0717px 8.57359px rgba(0, 0, 0, 0.05);
  border-radius: 18px;
}

[name="submit"]:focus,
[name="submit"]:hover {
  background-color: var(--discount-color);
}

@media screen and (min-width: 600px) {
  .tip,
  .calc__form--input {
    flex-direction: row;
  }
  .calc__form--input .input {
    width: 60%;
  }
  .calc__form--input .input + .input {
    width: 40%;
  }
}
!

JS 

              
                      const form = document.getElementById('calc__form');
      var tips = document.getElementsByName('tip');
      var total = document.querySelector('input[name="total"]');
      var nb = document.querySelector('input[name="nb-people"]');

      function calcTip(e) {

        for (i = 0; i < tips.length; i++) {
          if (tips[i].checked) {
            var tip = tips[i];
          }
        }

        var totalTip = document.querySelector('.tip__total--amount');
        var totalPerson = document.querySelector('.tip__pers--amount');

        totalTip.textContent = (total.value * tip.value).toFixed(2);
        totalPerson.textContent = (
          (total.value * tip.value) /
          nb.value
        ).toFixed(2);

        event.preventDefault();
      }

      form.addEventListener('submit', calcTip);
      total.addEventListener('change', calcTip);
      nb.addEventListener('change', calcTip);
      tips.forEach(radio => radio.addEventListener('change', calcTip));
!
999px

Console