/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-blue: #2196F3;
    --success-green: #4CAF50;
    --warning-yellow: #FFC107;
    --error-red: #F44336;
    --accent-purple: #9C27B0;
    --white: #FFFFFF;
    --light-gray: #F5F5F5;
    --dark-gray: #333333;
    --border-radius: 8px;
    --box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    --transition: all 0.3s ease;
}

body {
    font-family: 'Roboto', sans-serif;
    line-height: 1.6;
    color: var(--dark-gray);
    background-color: var(--light-gray);
}

/* Header Styles */
.header {
    background: linear-gradient(135deg, var(--primary-blue), var(--accent-purple));
    color: var(--white);
    padding: 2rem 0;
    text-align: center;
    box-shadow: var(--box-shadow);
}

.header__title {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.header__title i {
    margin-right: 0.5rem;
}

.header__subtitle {
    font-size: 1.2rem;
    font-weight: 300;
    opacity: 0.9;
}

/* Navigation Styles */
.nav {
    background: var(--white);
    box-shadow: var(--box-shadow);
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav__list {
    display: flex;
    list-style: none;
    justify-content: center;
    flex-wrap: wrap;
    padding: 1rem 0;
}

.nav__item {
    margin: 0 0.5rem;
}

.nav__button {
    background: transparent;
    border: 2px solid var(--primary-blue);
    color: var(--primary-blue);
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.nav__button:hover {
    background: var(--primary-blue);
    color: var(--white);
    transform: translateY(-2px);
}

.nav__button--active {
    background: var(--primary-blue);
    color: var(--white);
}

/* Main Content */
.main {
    padding: 2rem 0;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
}

/* Calculator Styles */
.calculator {
    background: var(--white);
    border-radius: var(--border-radius);
    box-shadow: var(--box-shadow);
    padding: 2rem;
    margin-bottom: 2rem;
}

.calculator__display {
    background: var(--dark-gray);
    color: var(--white);
    padding: 1.5rem;
    border-radius: var(--border-radius);
    margin-bottom: 1.5rem;
    min-height: 100px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
}

.display__history {
    font-size: 0.9rem;
    opacity: 0.7;
    margin-bottom: 0.5rem;
    min-height: 20px;
}

.display__result {
    font-size: 2rem;
    font-weight: 700;
    text-align: right;
    word-break: break-all;
}

.calculator__mode {
    display: none;
}

.calculator__mode--active {
    display: block;
}

.calculator__buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.75rem;
}

.calculator__buttons--scientific {
    grid-template-columns: repeat(5, 1fr);
}

/* Button Styles */
.btn {
    padding: 1rem;
    border: none;
    border-radius: var(--border-radius);
    font-size: 1.1rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
    min-height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--box-shadow);
}

.btn:active {
    transform: translateY(0);
}

.btn--number {
    background: var(--white);
    color: var(--dark-gray);
    border: 2px solid var(--light-gray);
}

.btn--number:hover {
    background: var(--light-gray);
}

.btn--operator {
    background: var(--primary-blue);
    color: var(--white);
}

.btn--operator:hover {
    background: #1976D2;
}

.btn--function {
    background: var(--success-green);
    color: var(--white);
}

.btn--function:hover {
    background: #388E3C;
}

.btn--equals {
    background: var(--warning-yellow);
    color: var(--dark-gray);
}

.btn--equals:hover {
    background: #F57C00;
    color: var(--white);
}

.btn--clear {
    background: var(--error-red);
    color: var(--white);
}

.btn--clear:hover {
    background: #C62828;
}

.btn--span-2 {
    grid-column: span 2;
}

/* Financial and Math Input Styles */
.financial-inputs,
.math-inputs {
    margin-bottom: 1.5rem;
}

.input-group {
    margin-bottom: 1rem;
}

.input-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: var(--dark-gray);
}

.form-control {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid var(--light-gray);
    border-radius: var(--border-radius);
    font-size: 1rem;
    transition: var(--transition);
}

.form-control:focus {
    outline: none;
    border-color: var(--primary-blue);
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

.financial-buttons,
.math-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 0.75rem;
}

/* Explanation Panel */
.explanation,
.history-panel {
    background: var(--white);
    border-radius: var(--border-radius);
    box-shadow: var(--box-shadow);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
}

.explanation__title,
.history-panel__title {
    color: var(--primary-blue);
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.explanation__content,
.history-panel__content {
    background: var(--light-gray);
    padding: 1rem;
    border-radius: var(--border-radius);
    max-height: 300px;
    overflow-y: auto;
}

.explanation__content p,
.history-panel__content p {
    margin-bottom: 0.5rem;
}

.explanation__content strong {
    color: var(--primary-blue);
}

/* FAQ Styles */
.faq {
    background: var(--white);
    padding: 3rem 0;
    margin-top: 2rem;
}

.faq__title {
    text-align: center;
    color: var(--primary-blue);
    margin-bottom: 2rem;
    font-size: 2rem;
}

.accordion-button {
    background: var(--light-gray);
    color: var(--dark-gray);
    border: none;
    font-weight: 500;
}

.accordion-button:not(.collapsed) {
    background: var(--primary-blue);
    color: var(--white);
}

.accordion-button:focus {
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

.accordion-body {
    background: var(--white);
    color: var(--dark-gray);
    line-height: 1.6;
}

/* Footer Styles */
.footer {
    background: var(--dark-gray);
    color: var(--white);
    padding: 2rem 0;
    text-align: center;
}

.footer__content {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1rem;
}

.footer__text {
    margin: 0;
}

.footer__text a {
    color: var(--primary-blue);
    text-decoration: none;
}

.footer__text a:hover {
    text-decoration: underline;
}

.footer__links {
    display: flex;
    gap: 1.5rem;
}

.footer__links a {
    color: var(--white);
    text-decoration: none;
    opacity: 0.8;
    transition: var(--transition);
}

.footer__links a:hover {
    opacity: 1;
    color: var(--primary-blue);
}

/* Responsive Design */
@media (max-width: 768px) {
    .header__title {
        font-size: 2rem;
    }
    
    .header__subtitle {
        font-size: 1rem;
    }
    
    .nav__list {
        flex-direction: column;
        align-items: center;
    }
    
    .nav__item {
        margin: 0.25rem 0;
        width: 100%;
        max-width: 200px;
    }
    
    .nav__button {
        width: 100%;
        justify-content: center;
    }
    
    .calculator {
        padding: 1rem;
    }
    
    .calculator__buttons {
        grid-template-columns: repeat(4, 1fr);
        gap: 0.5rem;
    }
    
    .calculator__buttons--scientific {
        grid-template-columns: repeat(4, 1fr);
    }
    
    .btn {
        padding: 0.75rem;
        font-size: 1rem;
        min-height: 50px;
    }
    
    .display__result {
        font-size: 1.5rem;
    }
    
    .financial-buttons,
    .math-buttons {
        grid-template-columns: 1fr;
    }
    
    .footer__content {
        flex-direction: column;
    }
    
    .footer__links {
        flex-direction: column;
        gap: 0.5rem;
    }
}

@media (max-width: 480px) {
    .header {
        padding: 1.5rem 0;
    }
    
    .header__title {
        font-size: 1.5rem;
    }
    
    .calculator__buttons {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .btn {
        padding: 0.5rem;
        font-size: 0.9rem;
        min-height: 45px;
    }
    
    .display__result {
        font-size: 1.2rem;
    }
}

/* Animation Classes */
.fade-in {
    animation: fadeIn 0.3s ease-in;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.shake {
    animation: shake 0.5s ease-in-out;
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}

/* Accessibility */
.btn:focus,
.form-control:focus,
.nav__button:focus {
    outline: 2px solid var(--primary-blue);
    outline-offset: 2px;
}

/* High contrast mode support */
@media (prefers-contrast: high) {
    :root {
        --light-gray: #E0E0E0;
        --dark-gray: #000000;
    }
    
    .btn {
        border: 2px solid currentColor;
    }
}

/* Reduced motion support */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}