style.css

body {
  box-sizing: border-box;
  display: flex;
  justify-content: center;
  background-color: red;
}

.bg {
  background-color: rgba(3, 3, 3, 0.815);
}

.container {
  display: flex;
  flex-direction: column;
  justify-content: space-around;
  width: auto;
  height: auto;
  border: none;
  border-radius: 10px;
}

.text-container {
  display: flex;
  justify-content: center;
  padding-top: 20px;
  margin-bottom: 20px;
}

#screen {
  width: 90%;
  height: 50px;
  border-radius: 5px;
  border: none;
  color: #fefefe;
  text-align: right;
  font-size: large;
  font-style: oblique;
  padding-right: 20px;

}

.button-container {
  display: flex;
  justify-content: space-around;
  margin-bottom: 15px;
}

.top-btn-container {
  margin: 20px 0;
}

.btns {
  color: #fefefe;
  font-family: 'Franklin Gothic Medium', 'Arial Narrow', Arial, sans-serif;
  font-size: large;
  font-style: italic;
  width: 40px;
  height: 30px;
  border: none;
  border-radius: 15px;
  box-shadow: 3px 3px 10px black;
  background-color: rgba(3, 3, 3, 0.1);
  cursor: pointer;
}

.changebg {
  background-color: #c9c0c0;
  border: none;
  color: black;
}

.btnEquals {
  display: flex;
  width: 90%;
  padding-top: 5px;
  justify-content: center;
}