* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
}

body {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background: linear-gradient(45deg, #ff6b6b, #4ecdc4);
    padding: 2rem;
}

.back-button {
    text-decoration: none;
    padding: 0.75rem 1.5rem;
    background: rgba(255, 255, 255, 0.1);
    color: white;
    border-radius: 10px;
    backdrop-filter: blur(5px);
    border: 1px solid rgba(255, 255, 255, 0.2);
    margin-bottom: 2rem;
    font-size: 1rem;
    transition: all 0.2s ease;
}

.back-button:hover {
    background: rgba(255, 255, 255, 0.2);
    transform: translateY(-2px);
}

.calculator-grid {
    position: relative;
}

.calculator {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    padding: 2rem;
    border-radius: 20px;
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.2);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
}

.output {
    grid-column: 1 / -1;
    background: rgba(255, 255, 255, 0.15);
    padding: 1.5rem;
    margin-bottom: 1rem;
    border-radius: 10px;
    text-align: right;
    word-wrap: break-word;
    word-break: break-all;
    border: 1px solid rgba(255, 255, 255, 0.2);
}

.previous-operand {
    color: rgba(255, 255, 255, 0.75);
    font-size: 1.2rem;
    min-height: 1.5rem;
}

.current-operand {
    color: white;
    font-size: 2.5rem;
    font-weight: 300;
}

button {
    font-size: 1.25rem;
    padding: 1rem;
    border: none;
    background: rgba(255, 255, 255, 0.1);
    color: white;
    border-radius: 10px;
    cursor: pointer;
    backdrop-filter: blur(5px);
    border: 1px solid rgba(255, 255, 255, 0.1);
    transition: all 0.2s ease;
}

button:hover {
    background: rgba(255, 255, 255, 0.2);
    transform: translateY(-2px);
}

button:active {
    transform: translateY(0);
}

.span-two {
    grid-column: span 2;
}

[data-action="="] {
    background: rgba(78, 205, 196, 0.2);
}

[data-action="="]:hover {
    background: rgba(78, 205, 196, 0.3);
}