* {
  margin: 0;
  padding: 0;

  -webkit-box-sizing: border-box;
     -moz-box-sizing: border-box;
          box-sizing: border-box;
}

body {
  height: 100vh;
  background-color: #34495E;
  background-repeat: no-repeat;

  font-family: monospace;
  display: flex;
  justify-content: center;
  align-items: center;
}

main {
  width: 80%;
  min-width: 320px;
  max-width: 640px;
  height: 80%;
  box-shadow: 2px 7px 10px rgba(0,0,0,0.6);
}

#display {
  height: 30%;
  width: 100%;
  font-size: 3rem;
  text-align: right;
  background-color: #F4F7F7;
  border: none;
}

.keypad {
  height: 70%;
  width: 100%;

  display: flex;
}

button {
  background-color: Transparent;
  background-repeat:no-repeat;
  border: none;
  cursor:pointer;
  overflow: hidden;
  outline:none;

  font-size: 1.8rem;
  color: #F4F7F7;
  }


.keypad > * {
  height: 100%;
  margin: 0px;
  border: none;
}

.number-area {
  flex-grow: 3;
  background-color: #AACFD0;
}

.operator-area {
  flex-grow: 1;
  background-color: #5DA0A2;
}

.number-area button {
  width: 30%;
  height: 25%;
}


.operator-area button {
  width: 100%;
  height: 20%;
}

@media only screen and (min-width: 961px) and (max-width: 1440px) {
  main {
    max-width: 640px;
    max-height: 960px;
  }

}

@media only screen and (min-width: 1441px) {
  main {
    max-width: 60%;
    max-height: 1440px;
  }
}