main.css

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: 'Roboto Mono', monospace;
  font-size: 1.5rem;
}

.calculator {
  display: grid;
  grid-template-columns: repeat(4, 100px);
  grid-template-rows: repeat(6, 100px);
  gap: 0.1rem;
  background-color: #000;
  width: 407px;
  margin: 1rem auto;
}

.screen {
  grid-column: 1 / 5;
  height: 2;
  color: #fff;
  text-align: right;
  padding-right: 0.5rem;
  display: flex;
  justify-content:  flex-end;
  align-items: center;

}

.btn {
  background-color: #ebebeb;
  border: none;
  cursor: pointer;
}
.btn:hover {
  filter: brightness(105%)
}
.btn:active {
  filter: brightness(95%)
}

.colored {
  background-color: #fcb870;
}

.size-l {
  grid-column: 1 / 3;
}
.size-xl {
  grid-column: 1 / 4;
}