:root {
    --bg-color: #0d1117;
    --card-bg: rgba(23, 28, 36, 0.8);
    --text-main: #ffffff;
    --accent-op: #ff9f0a;
    --accent-eq: #34c759;
    --btn-bg: rgba(255, 255, 255, 0.05);
}

body {
    background: radial-gradient(circle at center, #1c2531, #0d1117);
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    margin: 0;
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
}

.calculator-card {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    border: 1px solid rgba(255, 255, 255, 0.1);
    padding: 25px;
    border-radius: 32px;
    box-shadow: 0 40px 100px rgba(0,0,0,0.6);
    width: 350px;
}

.display {
    text-align: right;
    padding: 20px;
    background: rgba(0, 0, 0, 0.2);
    border-radius: 20px;
    margin-bottom: 25px;
    min-height: 100px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    overflow-x: auto; /*it will Handle long values */
}

#upper-display {
    color: rgba(255, 255, 255, 0.4);
    font-size: 0.9rem;
    margin-bottom: 5px;
    white-space: nowrap;
}

#main-display {
    color: var(--text-main);
    font-size: 2.5rem;
    font-weight: 500;
    white-space: nowrap;
}

.buttons-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

button {
    height: 65px;
    border-radius: 18px;
    border: none;
    background: var(--btn-bg);
    color: white;
    font-size: 1.3rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

button:hover {
    background: rgba(255, 255, 255, 0.15);
    transform: translateY(-2px);
}

button:active {
    transform: scale(0.95);
}

.btn-op { color: var(--accent-op); background: rgba(255, 159, 10, 0.1); }
.btn-alt { color: #ff453a; background: rgba(255, 69, 58, 0.1); }
.btn-equal { 
    background: var(--accent-eq); 
    color: white; 
    box-shadow: 0 10px 20px rgba(52, 199, 89, 0.3);
}
.btn-equal:hover { background: #30b350; }