style.css

body {  
    background-color: #110f0f;
    padding: 20px;
}

.grid-container {
    display: grid;
    align-items: center;
    justify-content: center; 
}

.calculator-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(6, 1fr);
    grid-gap: 1px;
	  background-color: #999;
} 

.calculator-grid button {
    font-size: 25px;
    background-color: #fff;
    border: none;
    cursor: pointer;
    font-family: 'DM Mono', monospace;
} 

textarea {
	grid-column: span 4;
  font-family: 'DM Mono', monospace;
	font-size: 25px;
	text-align: end;
	background-color: #fad3cb;
  padding: 15px;
  border: none;
}

.calculator-grid button:nth-child(n+18) {
    background-color: tomato; 
}


button:hover,
.calculator-grid button:nth-child(n+18):hover {
    background-color: #440b15;
    color: white;
    transition: 0.2s;
}
a:link, a:visited {
    background-color: #f44336;
    color: white;
    padding: 14px 25px;
    text-align: center;
    text-decoration: none;
    display: inline-block;
  }
  
  a:hover, a:active {
    background-color: red;
  }