simple-keyboard/src/demo/css/DOMElementDemo.css

input {
  width: 100%;
  height: 100px;
  padding: 20px;
  font-size: 20px;
  border: none;
  box-sizing: border-box;
}

.my-keyboard,
.my-keyboard2 {
  max-width: 850px;
  margin-top: 20px;
}