/* Using CSS variables for an easy-to-manage color scheme */
:root {
    --bg-color: #22252D;
    --calculator-bg: #292D36;
    --screen-bg: #292D36;
    --button-bg: #272B33;
    --operator-bg: #363a44;
    --equals-bg: #5f63bf;
    --text-color: #FFFFFF;
    --operator-text-color: #a3a6b0;
    --equals-text-color: #FFFFFF;
}

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

body {
    font-family: 'Poppins', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: var(--bg-color);
}

.calculator-body {
    width: 320px;
    background-color: var(--calculator-bg);
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
}

.calculator-screen {
    width: 100%;
    height: 80px;
    background-color: var(--screen-bg);
    color: var(--text-color);
    text-align: right;
    padding: 20px;
    font-size: 2.5rem;
    font-weight: 500;
    border-radius: 10px;
    margin-bottom: 20px;
    overflow-x: auto;
    /* For a cleaner scrollbar */
    scrollbar-width: thin;
    scrollbar-color: var(--operator-bg) var(--screen-bg);
}

/* Animation for when result is displayed */
.screen-result-animation {
    animation: fadeIn 0.3s ease-in-out;
}

@keyframes fadeIn {
    from { opacity: 0.5; transform: translateY(5px); }
    to { opacity: 1; transform: translateY(0); }
}

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

.button {
    height: 60px;
    border: none;
    border-radius: 10px;
    background-color: var(--button-bg);
    color: var(--text-color);
    font-size: 1.5rem;
    font-weight: 500;
    cursor: pointer;
    transition: background-color 0.2s, transform 0.1s;
}

.button:hover {
    background-color: #3a3f4c;
}

/* "Press down" animation */
.button:active {
    transform: scale(0.95);
}

/* Styling different button types */
.button.operator {
    background-color: var(--operator-bg);
    color: var(--operator-text-color);
}

.button.operator:hover {
    background-color: #494e5e;
}

.button.equals {
    background-color: var(--equals-bg);
    color: var(--equals-text-color);
    grid-column: span 2; /* Make the equals button wider */
}

.button.equals:hover {
    background-color: #4d4ea6;
}

.button.zero {
    grid-column: span 1;
}