* {
  margin: 0px;
  padding: 0px;
  box-sizing: border-box;
}
@font-face {
  font-family: digital;
  src: url(Digital.ttf);
}
body {
  display: flex;
  flex-direction: column;
  height: 100vh;
  width: 100vw;
  align-items: center;
  justify-content: center;
  background-color: lightblue;
}

#heading {
  font-family: digital;
  font-size: 30px;
  color: green;
  font-weight: bold;
}
form {
  padding: 20px;
  background-color: green;
  border-radius: 5px;
  box-shadow: 5px 5px 10px black;
}
#display {
  width: 265px;
  text-align: right;
  padding: 10px;
  margin-bottom: 10px;
  border-radius: 10px;
  font-size: 40px;
  background-color: black;
  color: green;
  font-family: digital;
}

.num_btn,
.opt_btn,
.fun_btn {
  height: 50px;
  margin-top: 5px;
  border-radius: 10px;
  font-size: 20px;
  box-shadow: 1px 1px 1px black;
}

.num_btn {
  width: 50px;
}
.opt_btn {
  width: 50px;
  background-color: yellow;
  /* color: white; */
}

.fun_btn {
  width: 104px;
  background-color: red;
  /* color: red; */
}