* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'DM Sans', sans-serif;
}

body {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

.calculator {
    background-color: #1e1e2e;
    padding: 22px;
    border-radius: 28px;
    box-shadow: 0px 30px 70px rgba(0, 0, 0, 0.35);
    width: 300px;
}

#display {
    width: 100%;
    height: 80px;
    background-color: #13131f;
    border: none;
    border-radius: 18px;
    margin-bottom: 18px;
    padding: 10px 18px;
    font-size: 2.2rem;
    font-weight: 400;
    text-align: right;
    color: #f0f0ff;
    outline: none;
    letter-spacing: -1px;
}

#display::placeholder {
    color: #555577;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

button {
    height: 62px;
    border: none;
    border-radius: 14px;
    font-family: 'DM Sans', sans-serif;
    font-size: 1.1rem;
    font-weight: 500;
    cursor: pointer;
    transition: transform 0.08s, filter 0.08s;
}

button:hover {
    filter: brightness(1.15);
}

button:active {
    transform: scale(0.92);
    filter: brightness(0.88);
}

.num {
    background-color: #2e2e42;
    color: #d0d0ee;
}

.op {
    background-color: #7c6ff7;
    color: #ffffff;
    font-size: 1.2rem;
}

.op.active-op {
    background-color: #4f44b8;
    box-shadow: inset 0 2px 6px rgba(0, 0, 0, 0.3);
}

.ac {
    background-color: #3d1f2a;
    color: #ff6b8a;
    font-size: 0.95rem;
    font-weight: 600;
}

.del {
    background-color: #2a2a40;
    color: #a0a0cc;
    font-size: 0.95rem;
    font-weight: 600;
}

.func {
    background-color: #2a3a4a;
    color: #7ab8d4;
    font-size: 0.95rem;
    font-weight: 600;
}

.equalBtn {
    background-color: #f7a035;
    color: #1a1000;
    font-size: 1.3rem;
    font-weight: 600;
    box-shadow: 0 6px 18px rgba(247, 160, 53, 0.4);
}

.equalBtn:hover {
    filter: brightness(1.1);
}