:root {
            --bg-color: #22252D;
            --keys-bg-color: #292D36;
            --display-bg-color: #22252D;
            --operator-key-color: #F38586;
            --special-key-color: #4E505F;
            --number-key-color: #2E303E;
            --text-light-color: #FFFFFF;
            --text-dark-color: #3B3B3B;
            --text-operator-color: #929292;
        }

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

        body {
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 100vh;
            background: linear-gradient(45deg, #3a3a3a, #1e1e1e);
        }

        .calculator {
            width: 100%;
            max-width: 375px;
            background-color: var(--bg-color);
            border-radius: 30px;
            box-shadow: 0 20px 40px rgba(0, 0, 0, 0.3);
            overflow: hidden;
            display: flex;
            flex-direction: column;
        }

        .calculator-display {
            background-color: var(--display-bg-color);
            color: var(--text-light-color);
            text-align: right;
            padding: 40px 30px;
            min-height: 150px;
            display: flex;
            flex-direction: column;
            justify-content: flex-end;
            word-wrap: break-word;
            word-break: break-all;
        }
        
        .display-history {
            font-size: 1.5rem;
            color: var(--text-operator-color);
            opacity: 0.7;
            height: 30px;
        }

        .display-current {
            font-size: 3.5rem;
            font-weight: 500;
        }

        .calculator-keys {
            display: grid;
            grid-template-columns: repeat(4, 1fr);
            gap: 15px;
            padding: 25px;
            background-color: var(--keys-bg-color);
            border-radius: 30px 30px 0 0;
        }

        button {
            border: none;
            background-color: var(--number-key-color);
            color: var(--text-light-color);
            font-size: 1.5rem;
            font-weight: 500;
            border-radius: 20px;
            height: 70px;
            cursor: pointer;
            transition: filter 0.2s ease;
            outline: none;
            box-shadow: 0 5px 10px rgba(0,0,0,0.1);
        }

        button:hover {
            filter: brightness(1.2);
        }

        button:active {
            filter: brightness(0.9);
            transform: translateY(2px);
            box-shadow: 0 2px 5px rgba(0,0,0,0.2);
        }

        .key-operator {
            background-color: var(--operator-key-color);
            color: var(--text-dark-color);
            font-size: 2rem;
        }
        
        .key-special {
             background-color: var(--special-key-color);
             color: var(--text-light-color);
        }
        
        .key-equal {
            background-color: var(--operator-key-color);
            color: var(--text-dark-color);
            grid-column: span 2;
            width: 100%;
        }