* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: 'Roboto', 'Segoe UI', Arial, sans-serif;
            background-color: #202124;
            min-height: 100vh;
            display: flex;
            flex-direction: column;
            align-items: center;
            padding: 20px;
            color: #e8eaed;
        }

        .calculator-container {
            width: 100%;
            max-width: 600px;
            background-color: #202124;
            border-radius: 20px;
            padding: 20px;
        }

        .display {
            background-color: #303134;
            border-radius: 12px;
            padding: 20px;
            margin-bottom: 20px;
            text-align: right;
            min-height: 80px;
            display: flex;
            flex-direction: column;
            justify-content: center;
        }

        .previous-operand {
            color: #9aa0a6;
            font-size: 18px;
            min-height: 24px;
            word-wrap: break-word;
        }

        .current-operand {
            color: #e8eaed;
            font-size: 42px;
            font-weight: 300;
            word-wrap: break-word;
            overflow-wrap: break-word;
        }

        .mode-toggle {
            display: flex;
            gap: 10px;
            margin-bottom: 15px;
            justify-content: flex-start;
        }

        .mode-btn {
            background: transparent;
            border: none;
            color: #9aa0a6;
            padding: 8px 16px;
            border-radius: 20px;
            cursor: pointer;
            font-size: 14px;
            transition: all 0.2s;
        }

        .mode-btn.active {
            background-color: #3c4043;
            color: #e8eaed;
        }

        .mode-btn:hover {
            background-color: #3c4043;
        }

        .buttons-grid {
            display: grid;
            grid-template-columns: repeat(4, 1fr);
            gap: 8px;
        }

        .btn {
            border: none;
            border-radius: 12px;
            padding: 20px;
            font-size: 18px;
            cursor: pointer;
            transition: all 0.15s;
            min-height: 56px;
            display: flex;
            align-items: center;
            justify-content: center;
        }

        .btn:active {
            transform: scale(0.95);
        }

        /* Number buttons */
        .btn-number {
            background-color: #3c4043;
            color: #e8eaed;
        }

        .btn-number:hover {
            background-color: #4a4d50;
        }

        /* Operator buttons */
        .btn-operator {
            background-color: #5f6368;
            color: #e8eaed;
        }

        .btn-operator:hover {
            background-color: #70757a;
        }

        /* Scientific function buttons */
        .btn-scientific {
            background-color: #303134;
            color: #9aa0a6;
            font-size: 16px;
        }

        .btn-scientific:hover {
            background-color: #3c4043;
            color: #e8eaed;
        }

        /* Equals button */
        .btn-equals {
            background-color: #8ab4f8;
            color: #202124;
            font-weight: 500;
        }

        .btn-equals:hover {
            background-color: #aecbfa;
        }

        /* Clear button */
        .btn-clear {
            background-color: #5f6368;
            color: #e8eaed;
        }

        /* Zero button spans 2 columns */
        .btn-zero {
            grid-column: span 1;
        }

        .scientific-row {
            display: contents;
        }

        .hidden {
            display: none;
        }

        @media (max-width: 480px) {
            .btn {
                padding: 16px;
                font-size: 16px;
                min-height: 48px;
            }
            
            .current-operand {
                font-size: 32px;
            }
        }