:root {
    --bg-color: #000000;
    --key-number-bg: #333333;
    --key-operator-bg: #ff9f0a;
    --key-functional-bg: #a5a5a5;
    --text-color: #ffffff;
    --text-dark: #000000;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    -webkit-tap-highlight-color: transparent;
    user-select: none;
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: hidden;
}

.calculator {
    width: 100%;
    max-width: 430px; /* iPhone 15 Pro Max width approximation */
    height: 100%;
    max-height: 932px;
    display: flex;
    flex-direction: column;
    padding: 20px 20px calc(20px + env(safe-area-inset-bottom));
    position: relative;
}

.header {
    display: flex;
    justify-content: space-between;
    padding: 20px 0;
    color: var(--text-color);
}

.icon-btn {
    background: none;
    border: none;
    color: inherit;
    padding: 10px;
    cursor: pointer;
    opacity: 0.8;
}

.display {
    flex: 1;
    display: flex;
    align-items: flex-end;
    justify-content: flex-end;
    padding: 20px 10px;
    margin-bottom: 10px;
}

.result {
    font-size: 80px;
    font-weight: 300;
    text-align: right;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: clip;
}

.keypad {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-gap: 12px;
}

.key {
    aspect-ratio: 1/1;
    border-radius: 50%;
    border: none;
    font-size: 32px;
    font-weight: 400;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    transition: filter 0.1s, transform 0.05s;
}

.key:active {
    filter: brightness(1.5);
    transform: scale(0.95);
}

.key.number {
    background-color: var(--key-number-bg);
    color: var(--text-color);
}

.key.functional {
    background-color: var(--key-functional-bg);
    color: var(--text-dark);
    font-size: 28px;
}

.key.operator {
    background-color: var(--key-operator-bg);
    color: var(--text-color);
    font-size: 36px;
}

.key.operator.active {
    background-color: var(--text-color);
    color: var(--key-operator-bg);
}

/* Specific button styles */
button[data-key="backspace"] svg {
    margin-left: -2px;
}

/* Mobile full screen adjustments */
@media (max-width: 480px) {
    .calculator {
        padding: 10px 10px calc(10px + env(safe-area-inset-bottom));
    }
    
    .result {
        font-size: 90px;
    }
}