* {
  box-sizing: border-box;
}

body {
  background-color: #333;
}

section {
  margin: auto;
  margin-top: 10px;
  /*border: 1px solid red;*/
  width: 800px;
  padding: 20px;
  border-radius: 30px;
  background-color: #111;
  box-shadow: 3px 3px 5px #00000050;
}

section .display {
  /*border: 1px solid green;*/
  height: 80px;
  margin-bottom: 20px;
  border-radius: 20px;
  background-color: #ddd;
  text-align: left;
  padding: 20px;
  font-size: 40px;
  line-height: 40px;
}

section .button-container {
  /*border: 1px solid white;*/
  position: relative;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  padding: 10px 90px;
  border-radius: 30px;
  background-color: #333;
}

section .button-container .btn {
  width: 100px;
  height: 100px;
  background-color: #666;
  margin: 10px 0;
  padding: 10px;
  border-radius: 10px;
  transition: .4s background-color;
  text-align: center;
  font-size: 40px;
  line-height: 80px;
  color: #fff;
  font-weight: bold;
}

section .button-container .btn:hover {
  background-color: #888;
}

section .button-container .btn.c,
section .button-container .btn.del {
  background-color: #cf3838;
}

section .button-container .btn.c:hover,
section .button-container .btn.del:hover {
  background-color: #db5151;
} 

section .button-container .author {
  /*border: 1px solid #fff;*/
  position: absolute;
  bottom: 3px;
  right: 25px;
  color: #222;
}