body {
    background: #f2f2f5;
    font-family: Arial, sans-serif;
    text-align: center;
}

/* TOP HEADER BAR */
.top-header {
    width: 100%;
    background: #0008ff;
    padding: 15px 0;
    color: white;
    font-size: 13px;
    font-weight: bold;
    position: relative;
}

.back-btn {
    position: absolute;
    left: 15px;
    top: 15px;
    text-decoration: none;
    color: white;
    font-size: 28px;
}

.green-line {
    width: 100%;
    height: 10px;
    background: #12ef06;
}

/* CALCULATOR */
.calculator-container {
    background: white;
    width: 350px;
    padding: 20px;
    margin: 40px auto;
    border-radius: 15px;
    box-shadow: 0px 0px 15px #bdbdbd;
}

#display {
    width: 100%;
    height: 60px;
    font-size: 28px;
    text-align: right;
    padding-right: 15px;
    margin-bottom: 20px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 10px;
}

button {
    padding: 15px;
    font-size: 18px;
    border: none;
    border-radius: 10px;
    background: #eaeaea;
    cursor: pointer;
}

button:hover {
    background: #d2d2d2;
}

.op {
    background: #006650;
    color: white;
}

.op:hover {
    background: #004c3b;
}

.equal {
    grid-column: span 3;
    background: #b30000;
    color: white;
}

.equal:hover {
    background: #7a0000;
}