html

    <h1>물 마시기</h1>
    <h3>목표 : 2L</h3>

    <div class="cup">
      <div class="remained" id="remained">
        <span id="liters"></span>
        <small>Remained</small>
      </div>

      <div class="percentage" id="percentage"></div>
    </div>

    <p class="text">마신 물컵의 숫자만큼 마우스 클릭으로 선택해 주세요</p>

    <div class="cups">
      <div class="cup cup-small">250 ml</div>
      <div class="cup cup-small">250 ml</div>
      <div class="cup cup-small">250 ml</div>
      <div class="cup cup-small">250 ml</div>
      <div class="cup cup-small">250 ml</div>
      <div class="cup cup-small">250 ml</div>
      <div class="cup cup-small">250 ml</div>
      <div class="cup cup-small">250 ml</div>
    </div>

css

@import url('https://fonts.googleapis.com/css?family=Montserrat:400,600&display=swap');

:root {
  --border-color: #144fc6;
  --fill-color: #6ab3f8;
}

* {
  box-sizing: border-box;
}

body {
  background-color: #3494e4;
  color: #fff;
  font-family: 'Montserrat', sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  margin-bottom: 40px;
}

h1 {
  margin: 10px 0 0;
}

h3 {
  font-weight: 400;
  margin: 10px 0;
}

.cup {
  background-color: #fff;
  border: 4px solid var(--border-color);
  color: var(--border-color);
  border-radius: 0 0 40px 40px;
  height: 330px;
  width: 150px;
  margin: 30px 0;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.cup.cup-small {
  height: 95px;
  width: 50px;
  border-radius: 0 0 15px 15px;
  background-color: rgba(255, 255, 255, 0.9);
  cursor: pointer;
  font-size: 14px;
  align-items: center;
  justify-content: center;
  text-align: center;
  margin: 5px;
  transition: 0.3s ease;
}

.cup.cup-small.full {
  background-color: var(--fill-color);
  color: #fff;
}

.cups {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  width: 280px;
}

.remained {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  flex: 1;
  transition: 0.3s ease;
}

.remained span {
  font-size: 20px;
  font-weight: bold;
}

.remained small {
  font-size: 12px;
}

.percentage {
  background-color: var(--fill-color);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: bold;
  font-size: 30px;
  height: 0;
  transition: 0.3s ease;
}

.text {
  text-align: center;
  margin: 0 0 5px;
}