style.scss

* {
  box-sizing: border-box;
  border-radius: 5px;
}

.App {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
  padding: 0;
  background: #e9e9e9;
}

#clock {
  display: flex;
  width: 500px;
  background: #333;
  padding: 20px;
  color: #fff;
  font-weight: bold;
  font-family: sans-serif;
  & div > div {
    display: flex;
    align-items: center;
    &:nth-child(3) {
      background: #000;
      padding: 0.25rem;
    }
    > div {
      margin: 0.5rem;
    }
    i {
      cursor: pointer;
      transition: transform 0.3s ease-in;
      &:hover {
        transform: scale(1.05);
      }
      &:active {
        transform: scale(0.75);
      }
    }
  }

  #session-length,
  #break-length {
    width: 25.8px;
    display: flex;
    justify-content: center;
  }

  .second-column {
    margin-left: 1.1rem;
    #display {
      align-self: center;
      background: #000;
      display: flex;
      flex-direction: column;
      width: 180px;
      div:first-child {
        align-self: flex-start;
      }
      div:last-child {
        align-self: center;
        font-size: 1.5rem;
        margin-top: 0.5rem;
      }
    }

    #start_stop {
      margin-top: 0.5rem;
    }

    #buttons {
      background: #939393;
      display: flex;
      justify-content: space-around;
    }
  }
}