* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: linear-gradient(135deg, #1a1a2e, #16213e);
}

/* ========== INSTALL BUTTON ========== */
.install-btn {
    position: fixed;
    top: 15px;
    right: 15px;
    z-index: 1000;
    background: #e94560;
    color: white;
    border: none;
    padding: 12px 18px;
    font-size: 1rem;
    font-weight: bold;
    border-radius: 25px;
    box-shadow: 0 4px 12px rgba(233, 69, 96, 0.4);
    cursor: pointer;
    animation: pulse 2s infinite;
}

.install-btn:active {
    transform: scale(0.95);
}

@keyframes pulse {
    0%, 100% { box-shadow: 0 4px 12px rgba(233, 69, 96, 0.4); }
    50% { box-shadow: 0 4px 20px rgba(233, 69, 96, 0.7); }
}

/* ========== CALCULATOR ========== */
.calculator {
    background: #0f3460;
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 15px 30px rgba(0, 0, 0, 0.4);
    width: 320px;
}

.display {
    background: #1a1a2e;
    color: #e94560;
    font-size: 2.2rem;
    text-align: right;
    padding: 20px;
    border-radius: 12px;
    margin-bottom: 20px;
    min-height: 80px;
    word-wrap: break-word;
    overflow: hidden;
}

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

.btn {
    background: #1a1a2e;
    color: #ffffff;
    border: none;
    padding: 18px;
    font-size: 1.2rem;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.2s ease;
}

.btn:hover {
    background: #16213e;
    transform: scale(0.95);
}

.btn:active {
    transform: scale(0.9);
}

.operator {
    background: #e94560;
    color: white;
}

.operator:hover {
    background: #c73e54;
}

.equal {
    background: #0f3460;
    border: 2px solid #e94560;
    color: #e94560;
    grid-column: span 2;
}

.equal:hover {
    background: #e94560;
    color: white;
}

.clear {
    background: #533483;
    color: white;
}

.clear:hover {
    background: #3d2563;
}