body {
   height: 100vh;
   width: 100%;
   background-image: linear-gradient(40deg, #00b0b3, #00CED1);
   background-position: cover;
   background-repeat: no-repeat;
   color: white;
   font: normal 15pt Arial;
}
* {
  margin: 0;
  padding: 0;
}
.button {
    background-color: #a8a8a8;
    border-radius: 10px;
    border: none;
    color: white;
    width: 70px;
    height: 70px;
    font-size: 30px;
    cursor: pointer;
}
.button:hover {
    background-color: #878787;
    box-shadow: 9px;
}
div#res {
  background-color: #d1d1d1;
  transition: background-color 0.5s ease;
  color: #575757;
  border-radius: 10px;
  width: 295px;
  height: 40px;
  line-height: 40px;
  text-align: center;
  font-size: 30px;
}
.calc {
    background-color: #64c47c;
    border-radius: 10px;
    border: none;
    color: white;
    width: 70px;
    height: 70px;
    font-size: 30px;
    cursor: pointer;
}
.calc:hover {
    background-color: #56ae6c;
    box-shadow: 9px;
}
.operad {
    background-color: #d67171;
    border-radius: 10px;
    border: none;
    color: white;
    width: 70px;
    height: 70px;
    font-size: 30px;
    cursor: pointer;
}
.operad:hover {
    background-color: #aa5555;
    
    box-shadow: 9px;
}
.clean {
  background-color: #71c1d6;
  border-radius: 10px;
  border: none;
  color: white;
  width: 70px;
  height: 70px;
  font-size: 30px;
  cursor: pointer;
}
.clean:hover {
  background-color: #65b0c3;
  box-shadow: 9px;
}

@media screen and (max-width: 500px) {
  * {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
  }
  body {
    height: 100%;
    width: 100%;
  }
  .main h2 {
    bottom: 85%; /* tamanho para telas menores */
  }
  }