<section class="checkout">
  <h1 class="header">Checkout</h1>
  <form class="checkout-form">
    <div class="input-group">
      <label class="label" for="name">Name:</label>
      <input type="text" class="input" name="name">
    </div>
    <div class="input-group">
      <label class="label" for="number">Card Number:</label>
      <input type="text" class="input" name="number">
    </div>
    <div class="input-group double">
      <div class="separator">
        <label for="date" class="label">Expiration Date:</label>
        <div class="inputs">
          <input type="text" class="input month" name="date" placeholder="MM">
          <span class="slash">/</span>
          <input type="text" class="input" name="date" placeholder="YY">
        </div>
      </div>
      <div class="separator">
        <label class="label" for="ccv">CCV:</label>
        <input type="text" class="input" name="ccv">
      </div>
    </div>
    <div class="btn-cont">
      <button type="submit" class="button">Checkout</button>
    </div>
  </form>
</section>

@import url("https://fonts.googleapis.com/css2?family=Roboto:wght@400;500;700&display=swap");

* {
  box-sizing: border-box;
  margin: 0;
}

:root {
  --light: #f9f9f9;
  --dark: #1f1f1f;
  --main: #2a9d8f;
  --main-hover: #228176;
}

body {
  width: 100vw;
  height: 100vh;
  display: flex;
  font-family: "Roboto", sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--light);
}

.checkout {
  width: 70%;
  max-width: 800px;
  min-width: 300px;
  height: 500px;
  background: var(--dark);
  color: var(--light);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  box-shadow: 2px 2px 20px rgba(0, 0, 0, 0.8);
}

.header {
  font-size: 30px;
  margin-bottom: 20px;
}

.input-group {
  width: 100%;
  padding: 20px 30px;
}

.label {
  color: var(--main);
  text-transform: uppercase;
  display: block;
  font-size: 14px;
  margin-bottom: 5px;
}

.input {
  font-family: inherit;
  background: none;
  border: none;
  border-radius: 0px;
  border-bottom: 1px solid var(--main);
  width: 100%;
  color: var(--light);
  font-size: 16px;
  position: relative;
}

.input::placeholder {
  color: var(--main);
}

.input:focus {
  outline: none;
  border-bottom-color: var(--light);
}

.input:focus::placeholder {
  color: var(--light);
}

.input-group.double {
  display: flex;
  justify-content: space-between;
}

.separator:nth-child(1) {
  width: 45%;
  padding-right: 20px;
}

.separator:nth-child(2) {
  width: 45%;
  padding-left: 20px;
}

.inputs {
  display: flex;
  justify-content: space-between;
}

.inputs .input {
  width: 45%;
  text-align: center;
}

.slash {
  color: var(--main);
  font-size: 18px;
}

.btn-cont {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-top: 20px;
}

.button {
  background: var(--main);
  border: none;
  border-radius: 0px;
  width: 50%;
  font-family: inherit;
  color: var(--light);
  font-size: 18px;
  padding: 15px 20px;
  cursor: pointer;
}

.button:hover {
  background: var(--main-hover);
}