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

html, body {
  height: 100%;
  width: 100%;
}
#myBox{
    background-color: greenyellow;
    width: 300px;
    height: 300px;
    font-size: 4.5rem;
    font-weight: bold;
    display: flex;
    align-items: center;
    text-align: center;
}

#mybutton{
    font-size: 2rem;
    margin-top: 2rem;
    margin-left: 4rem;
    padding: 10px 19px;
    border-radius: 10px;
    background-color: hsl(230, 81%, 58%);
    color: white;
    border: none;
    cursor: pointer;
}