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

body {
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%);
    padding: 20px;
}

.calculator {
    background: linear-gradient(145deg, #2c3e50, #34495e);
    border-radius: 15px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
    padding: 25px;
    width: 100%;
    max-width: 450px;
    position: relative;
}

.header {
    background: #1a252f;
    padding: 12px 15px;
    border-radius: 8px 8px 0 0;
    margin: -25px -25px 15px -25px;
    border-bottom: 2px solid #3498db;
}

.brand {
    color: #3498db;
    font-size: 0.95rem;
    font-weight: bold;
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: 5px;
}

.mode-indicator {
    display: flex;
    gap: 15px;
    font-size: 0.75rem;
    color: #95a5a6;
}

.mode-indicator span {
    padding: 2px 6px;
    background: rgba(52, 152, 219, 0.2);
    border-radius: 3px;
}

.display {
    background: #1a252f;
    border-radius: 8px;
    padding: 15px;
    margin-bottom: 20px;
    border: 2px solid #2c3e50;
    box-shadow: inset 0 2px 8px rgba(0, 0, 0, 0.3);
}

.status-line {
    display: flex;
    justify-content: space-between;
    color: #3498db;
    font-size: 0.75rem;
    min-height: 18px;
    margin-bottom: 8px;
    font-weight: 500;
}

.main-display {
    color: #ecf0f1;
    font-size: 2.2rem;
    font-weight: 400;
    text-align: right;
    min-height: 50px;
    word-wrap: break-word;
    word-break: break-all;
    font-family: 'Courier New', monospace;
    letter-spacing: 1px;
}

.button-row {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 8px;
    margin-bottom: 8px;
}

button {
    border: none;
    border-radius: 6px;
    font-size: 0.85rem;
    padding: 15px 8px;
    cursor: pointer;
    transition: all 0.15s;
    font-weight: 600;
    position: relative;
    box-shadow: 0 3px 0 rgba(0, 0, 0, 0.3);
}

button:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 0 rgba(0, 0, 0, 0.3);
}

button:active {
    transform: translateY(1px);
    box-shadow: 0 1px 0 rgba(0, 0, 0, 0.3);
}

button::after {
    content: attr(data-shift);
    position: absolute;
    top: 3px;
    left: 50%;
    transform: translateX(-50%);
    font-size: 0.65rem;
    color: #f39c12;
    font-weight: 500;
}

.number {
    background: linear-gradient(145deg, #95a5a6, #7f8c8d);
    color: #000;
}

.number:hover {
    background: linear-gradient(145deg, #a8b8b9, #8a9799);
}

.zero {
    grid-column: span 1;
}

.financial-key {
    background: linear-gradient(145deg, #3498db, #2980b9);
    color: #fff;
    font-size: 0.8rem;
}

.financial-key:hover {
    background: linear-gradient(145deg, #5dade2, #3498db);
}

.shift-key {
    background: linear-gradient(145deg, #e74c3c, #c0392b);
    color: #fff;
}

.shift-key:hover {
    background: linear-gradient(145deg, #ec7063, #e74c3c);
}

.shift-key.active {
    background: linear-gradient(145deg, #f39c12, #e67e22);
    box-shadow: 0 0 15px #f39c12;
}

.function-key {
    background: linear-gradient(145deg, #16a085, #138f77);
    color: #fff;
}

.function-key:hover {
    background: linear-gradient(145deg, #1abc9c, #16a085);
}

.function-key.clear {
    background: linear-gradient(145deg, #e74c3c, #c0392b);
}

.function-key.clear:hover {
    background: linear-gradient(145deg, #ec7063, #e74c3c);
}

.operator-key {
    background: linear-gradient(145deg, #e67e22, #d35400);
    color: #fff;
}

.operator-key:hover {
    background: linear-gradient(145deg, #f39c12, #e67e22);
}

.decimal {
    background: linear-gradient(145deg, #95a5a6, #7f8c8d);
    color: #000;
    font-weight: bold;
    font-size: 1.5rem;
}

.equals {
    background: linear-gradient(145deg, #27ae60, #229954);
    color: #fff;
    font-size: 1.2rem;
}

.equals:hover {
    background: linear-gradient(145deg, #2ecc71, #27ae60);
}

.help-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
    width: 35px;
    height: 35px;
    border-radius: 50%;
    background: linear-gradient(145deg, #3498db, #2980b9);
    color: #fff;
    font-size: 1.2rem;
    font-weight: bold;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 0;
    box-shadow: 0 3px 10px rgba(0, 0, 0, 0.3);
    z-index: 100;
}

.help-panel {
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background: #34495e;
    border: 3px solid #3498db;
    border-radius: 15px;
    padding: 25px;
    max-width: 500px;
    width: 90%;
    max-height: 80vh;
    overflow-y: auto;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.7);
    z-index: 1000;
    display: none;
}

.help-panel.active {
    display: block;
}

.help-panel h3 {
    color: #3498db;
    margin-bottom: 20px;
    font-size: 1.5rem;
    border-bottom: 2px solid #3498db;
    padding-bottom: 10px;
}

.help-section {
    margin-bottom: 20px;
}

.help-section h4 {
    color: #ecf0f1;
    margin-bottom: 10px;
    font-size: 1.1rem;
}

.help-section p {
    color: #bdc3c7;
    margin-bottom: 5px;
    line-height: 1.6;
}

/* Responsive design */
@media (max-width: 480px) {
    .calculator {
        padding: 15px;
        max-width: 100%;
    }

    button {
        padding: 12px 6px;
        font-size: 0.75rem;
    }

    .main-display {
        font-size: 1.8rem;
    }

    .financial-key {
        font-size: 0.7rem;
    }
}

/* Scrollbar styling for help panel */
.help-panel::-webkit-scrollbar {
    width: 8px;
}

.help-panel::-webkit-scrollbar-track {
    background: #2c3e50;
    border-radius: 10px;
}

.help-panel::-webkit-scrollbar-thumb {
    background: #3498db;
    border-radius: 10px;
}

.help-panel::-webkit-scrollbar-thumb:hover {
    background: #5dade2;
}