cover.css

*,
*:before,
*:after{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

body{
  background: #e0e5ec;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  font-family: 'Roboto', sans-serif;
}

.container{
    display: flex;
    flex-direction: column;
    align-items: center;
    flex-wrap: wrap;
    background-color: #ffffff;
    width: 40%;
    min-width: 500px;
    padding: 30px 0;
    border-radius: 10px;
    background: #ffffff;
    box-shadow:  20px 20px 60px #bebebe,
             -20px -20px 60px #ffffff;
}

.displayTimer{
    width: 90%;
    background: #ffffff;
    box-shadow:  20px 20px 60px #bebebe,
             -20px -20px 60px #ffffff;
    padding: 40px 0;
    font-size: 55px;
    display: flex;
    justify-content: space-around;
    border-radius: 5px;
}

.buttons{
    width: 90%;
    margin: 30px auto 0 auto;
    display: flex;
    justify-content: space-around;
}

button{
    width: 120px;
    height: 45px;
    background: #ffffff;
    box-shadow:  20px 20px 60px #bebebe,
             -20px -20px 60px #ffffff;
    border: none;
    font-size: 18px;
    border-radius: 5px;
    cursor: pointer;
    outline: none;
}

button:hover{
    box-shadow:  4px 4px 6px 0 rgba(255,255,255,.5),
                -4px -4px 6px 0 rgba(116, 125, 136, .2), 
      inset -4px -4px 6px 0 rgba(255,255,255,.5),
      inset 4px 4px 6px 0 rgba(116, 125, 136, .3);
  }

  @media all and (max-width: 500px) {
    .container{
        min-width: 320px;
    }

    .displayTimer{
        font-size: 35px;
    }

    .buttons{
        flex-direction: column;
        align-items: center;
    }

    button{
        margin: 10px;
    }
    
  }