<div class='calc'>
  <button value="+" class="operation">+</button>
  <button value="-" class="operation">−</button>
  <button value="*" class="operation">×</button>
  <button value="/" class="operation">÷</button>
  <button value="7">7</button>
  <button value="8">8</button>
  <button value="9">9</button>
  <button value="4">4</button>
  <button value="5">5</button>
  <button value="6">6</button>
  <button value="1">1</button>
  <button value="2">2</button>
  <button value="3">3</button>
  <button value="0">0</button>
  <button value=".">.</button>
  <button value="C" class="clear">C</button>
  <button value='=' class="right operation">=</button>
</div>

.calc {
  display: grid;
  grid-template-columns: repeat(4, 40px);
  grid-auto-rows: 40px;
  grid-gap: 10px;
}

.right {
  grid-column-start: 4;
  grid-row-start: 2;
  grid-row-end: 6;
}

button {
  border: 1px solid #888;
  border-radius: 10px;
  cursor: pointer;
  box-shadow: 2px 2px #888;
  transition: 0.1s ease-out;
}

.operation {
  background-color: #AAF;
}

.clear {
  background-color: #FAA;
}

button:hover {
  filter: brightness(0.8);
}

button:active {
  transform: translate(2px, 2px);
  box-shadow: 1px 1px;
}