/* Basic Reset */
* {
    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-color: #222; 
}

/* Main Calculator Box */
.calculator-container {
    background-color: #333;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.5);
    width: 100%;
    max-width: 350px;
}

/* Display Screen */
.display-screen {
    margin-bottom: 20px;
}

.display-screen input {
    width: 100%;
    height: 60px;
    background-color: #ecf0f3;
    border: none;
    border-radius: 8px;
    text-align: right;
    padding: 10px 20px;
    font-size: 2rem;
    color: #333;
    outline: none;
    box-shadow: inset 2px 2px 5px #cbced1,
                inset -5px -5px 10px #ffffff;
}

/* Buttons Layout */
.buttons-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

/* Button Styling */
.btn {
    border: none;
    padding: 15px;
    font-size: 1.2rem;
    border-radius: 10px;
    cursor: pointer;
    background-color: #444;
    color: white;
    box-shadow: 3px 3px 5px rgba(0,0,0,0.2);
    transition: transform 0.1s ease, background-color 0.2s;
}

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

.btn:hover {
    background-color: #555;
}


.btn.operator {
    background-color: #ff9f43;
    color: #fff;
    font-weight: bold;
}

.btn.operator:hover {
    background-color: #ffaf63;
}

/* Equal Button */
.equal-btn {
    grid-row: span 2; 
    background-color: #2ecc71;
    height: 100%;
}

.equal-btn:hover {
    background-color: #27ae60;
}

/* Zero button styling adjustment */
.zero-btn {
    grid-column: span 2; 
}