style.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: "Segoe UI", Verdana, sans-serif;
  color: white;
}

.container {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background-color: #202020;
  width: 20rem;
  border-radius: 15px;
}

.calculator-container {
  padding: 6px;
}

.top-bar {
  cursor: grab;
  height: 30px;
  border-bottom: 1px solid grey;
  border-top-left-radius: 15px;
  border-top-right-radius: 15px;
  background-color: #333;
  user-select: none;
}

.preview {
  min-height: 8rem;
  width: 100%;

  display: flex;
  flex-direction: column;
  align-items: flex-end;
  justify-content: center;
  padding: 10px;
}

.preview .value {
  font-size: 2.5rem;
  font-weight: bold;
  overflow-wrap: break-word;

  width: 100%;
  text-align: end;
}

.preview .operations {
  color: #8e8e8e;
  padding-bottom: 5px;
  height: 30px;
  overflow-x: auto;
  overflow-wrap: break-word;
  width: 100%;
  margin-bottom: 20px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
}

.buttons .btn {
  height: 50px;
  margin: 1.2px;
  background-color: #323232;
  border-radius: 5px;

  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 1.15rem;
  user-select: none;
}

.btn:hover {
  background-color: #3e3e3e;
}

.buttons .btn.number,
.btn.oper_num {
  background-color: #3e3e3e;
}

.btn.number:hover,
.btn.oper_num:hover {
  background-color: #323232;
}

#equal {
  background-color: #d0cdf0;
  color: black;
}

#equal:hover {
  background-color: rgba(180, 176, 215, 0.9);
}

#square sup {
  font-size: 0.575rem;
}