odin-calculator/style.css

body {
    display: flex;
    text-align: center;
    flex-direction: column;
    height: 100vh;
    margin: 0;
    background-color: #094909;
    color: #eee;
}

header {
    flex: 0 0 auto;
}

main {
    flex: 1;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

.calculator {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: auto;
    grid-gap: 5px;
    background: #594859;
    padding: 10px;
    box-shadow: 1px 2px 10px 1px #222;
}

.display {
    grid-column: 1 / span 4;
    height: 100px;
    max-width: 415px;
    overflow: hidden;
    background: #eee;
    color: #111;
    text-align: right;
    display: flex;
    flex-direction: column;
}
.top-screen {
    height: 40%;
    font-size: 20px;
}
.main-screen {
    height: 60%;
    font-size: 50px;
}

button {
    height: 100px;
    width: 100px;
    font-size: 50px;
    border-color: #eee;
    border-radius: 5px;
    box-shadow: 1px 2px 10px 1px #222;
    cursor: pointer;
}

button:hover {
    filter: brightness(.9);
}

button:active, .active {
    filter: brightness(.9);
    border: 1px solid #888; 
    box-shadow: inset 0 0 5px rgba(0, 0, 0, 0.3); 
}

.tooltip .tooltiptext {
    visibility: hidden;
    position: absolute;
    bottom: 115%;
    right: -15%;
    z-index: 1;

    width: 120px;
    font-size: 20px;
    background: #094909;
    color: #eee;
    opacity: 0;
    transition: opacity 0.7s;
    padding: 5px;
    border-radius: 5px;
}

/* Tooltip arrow */
.tooltip .tooltiptext::after {
    content: "";
    position: absolute;
    top: 100%;
    left: 50%;
    margin-left: -5px;
    border-width: 5px;
    border-style: solid;
    border-color: #094909 transparent transparent transparent;
  }

.tooltip:hover .tooltiptext, .tooltip:focus .tooltiptext {
    visibility: visible;
    opacity: 1;
}

.num, .plus-minus {
    background: #d9e1f2;
}

.clear {
    background: #f98383;
}

.operator {
    background: #ffff69;
}

.equal {
    grid-column: span 2;
    width: 205px;
    background: #79ff54;
}

footer {
    flex: 0 0 auto;
}