* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: Helvetica;

}

body {
  background-color: #333;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 3em;

}

#calc {
  width: 400px;
   padding: 0.5em;
   background-color: #c4c4c4;
   color: #000;
   display: flex;
   flex-direction: column;
 }

#calc h3 {
  font-size: 0.8em;
  font-weight: 300;
  color: #666;
}


#operations {
text-align: right;
}

#previous-operation {
color: #777;
padding: 0.2em;
overflow-wrap: break-word;
min-height: 1.6em;
}

#current-operation {
min-height: 1.6em;
font-size: 3em;
font-weight: 700;
padding: 0.2em;
overflow-wrap: break-word;
}

#buttons-container {
display: grid;
grid-template-columns: 1fr 1fr 1fr 1fr;
gap: 3px;
}

#buttons-container button {
border: 1px solid transparent;
border-radius: 0;
height: 4em;
font-size: 1.2em;
background-color: #dbdbdb;
cursor: pointer;
}

#buttons-container .number {
background-color: #f3f3f3;
}

#buttons-container button:hover {
background-color: #bababa;
border-color: #999;
}

#buttons-container #equal-btn {
grid-column: span 2;
background-color: #75a5cb;
}

#buttons-container #equal-btn:hover {
grid-column: span 2;
background-color: #3a91d8;
}