:root {
    --bg-light: #fff7f1;
    --card-light: #ffeabf;
    --text-light: #f8f4f4;
    --primary-light: #9b465b;
    --secondary-light: #3b8e97;

    --bg-dark: #2c2c2c;
    --card-dark: #44475a;
    --text-dark: #000000;
    --primary-dark: #8be9fd;
    --secondary-dark: #ffb86c;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    /* Using 'Inter' as per instructions, fallback to 'Quicksand' if not available */
    font-family: 'Inter', 'Quicksand', sans-serif;
    transition: all 0.3s ease;
}

body {
    background-color: var(--bg-light);
    color: var(--text-light);
    display: flex;
    /* Stack elements vertically */
    flex-direction: column;
    /* Center content vertically */
    justify-content: center;
    /* Center content horizontally */
    align-items: center;
    /* Ensure body takes full viewport height */
    min-height: 100vh; /* Use min-height to allow content to push body height if needed */
    padding: 1rem; /* Consistent padding around the content */
    overflow-x: hidden; /* Prevent horizontal scrollbar on small screens */
}

body.dark {
    background-color: var(--bg-dark);
    color: var(--text-dark);
}

#theme-toggle {
    background: var(--secondary-light);
    color: var(--text-light);
    border: none;
    padding: 0.5rem 1.2rem;
    border-radius: 25px;
    cursor: pointer;
    font-weight: bold;
    font-size: 1rem; /* Relative unit for font size */
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
    /* Space between calculator and button */
    margin-top: 1.5rem;
    /* Ensure the button doesn't shrink on smaller screens */
    flex-shrink: 0;
	max-width: 200px;
}

body.dark #theme-toggle {
    background: var(--secondary-dark);
    color: var(--text-dark);
}

#calculator {
    background-color: var(--card-light);
    border-radius: 20px;
    padding: 1.5rem; /* Consistent padding */
    box-shadow: 0 10px 20px rgba(0,0,0,0.1);
    max-width: 400px; /* Max width for larger screens */
    width: 100%; /* Take full width on smaller screens */
    /* Ensure the calculator doesn't shrink on smaller screens */
    flex-shrink: 0;
    /* Add a bit of margin-bottom for spacing if content below is added */
    margin-bottom: 1.5rem;
}

body.dark #calculator {
    background-color: var(--card-dark);
    box-shadow: 0 0 15px rgba(255, 255, 255, 0.1);
}

#display {
    width: 100%;
    height: 60px; /* Fixed height for consistency */
    background: var(--primary-light);
    color: var(--text-light);
    border: none;
    border-radius: 10px;
    font-size: 2rem; /* Relative unit for font size */
    padding: 0.5rem 1rem; /* Consistent padding */
    text-align: right;
    margin-bottom: 1rem;
}

body.dark #display {
    background: var(--primary-dark);
    color: var(--text-dark);
}

#keys {
    display: grid;
    /* Use 1fr for flexible column sizing */
    grid-template-columns: repeat(4, 1fr);
    gap: 0.75rem; /* Consistent gap between buttons */
}

button {
    padding: 1rem; /* Consistent padding */
    font-size: 1.25rem; /* Relative unit for font size */
    border: none;
    border-radius: 12px;
    cursor: pointer;
    background-color: var(--secondary-light);
    color: var(--text-light);
    font-weight: bold;
    /* Ensure buttons fill their grid cell */
    width: 100%;
    height: auto; /* Allow height to adjust based on content/padding */
}

button.operator-btn {
    background-color: var(--primary-light);
}

button:hover {
    transform: scale(1.05); /* Subtle scale effect on hover */
    opacity: 0.9;
}

body.dark button {
    background-color: var(--secondary-dark);
    color: var(--text-dark);
}

body.dark button.operator-btn {
    background-color: var(--primary-dark);
}

/* Media queries for fine-tuning on smaller screens */
@media (max-width: 480px) {
    #calculator {
        padding: 1rem; /* Slightly less padding on very small screens */
    }
    #display {
        font-size: 1.8rem; /* Adjust font size for display on small screens */
        height: 55px;
    }
    button {
        font-size: 1.1rem; /* Adjust button font size on small screens */
        padding: 0.8rem;
    }
    #theme-toggle {
        font-size: 0.9rem; /* Adjust theme toggle font size */
        padding: 0.4rem 1rem; /* Adjust theme toggle padding */
    }
}

@media (max-width: 320px) {
    #calculator {
        padding: 0.75rem; /* Even less padding on extremely small screens */
    }
    #display {
        font-size: 1.6rem;
        height: 50px;
    }
    button {
        font-size: 1rem;
        padding: 0.6rem;
    }
    #theme-toggle {
        font-size: 0.8rem; /* Further adjust theme toggle font size */
        padding: 0.3rem 0.8rem; /* Further adjust theme toggle padding */
    }
}