/* Base styles and variables */
:root {
    --primary-color: #2c3e50;
    --secondary-color: #34495e;
    --accent-color: #3498db;
    --text-color: #2c3e50;
    --error-color: #e74c3c;
    --success-color: #27ae60;
    --warning-color: #f39c12;
    --background-color: #f8f9fa;
    --border-radius: 4px;
    --spacing-unit: 1rem;
}

/* Reset and base styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--background-color);
    padding: var(--spacing-unit);
}

/* Container and layout */
.container {
    max-width: 800px;
    margin: 0 auto;
    padding: var(--spacing-unit);
    background-color: white;
    border-radius: var(--border-radius);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

header {
    margin-bottom: 2rem;
    text-align: center;
}

h1 {
    color: var(--primary-color);
    font-size: 1.8rem;
    margin-bottom: var(--spacing-unit);
}

h2 {
    color: var(--secondary-color);
    font-size: 1.4rem;
    margin-bottom: var(--spacing-unit);
}

/* Calculator section */
.calculator {
    margin-bottom: 2rem;
}

.input-group {
    margin-bottom: 1.5rem;
}

label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
}

input, select, button {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid #ddd;
    border-radius: var(--border-radius);
    font-size: 1rem;
}

input:focus, select:focus {
    outline: none;
    border-color: var(--accent-color);
    box-shadow: 0 0 0 2px rgba(52, 152, 219, 0.2);
}

.help-text {
    display: block;
    margin-top: 0.25rem;
    color: #666;
    font-size: 0.875rem;
}

.fstop-input-container {
    display: grid;
    grid-template-columns: 1fr auto;
    gap: 1rem;
    margin-bottom: 0.5rem;
}

/* Filters */
.filters-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
    margin-bottom: 1rem;
}

.filter-group {
    display: flex;
    flex-direction: column;
}

.filter-group label {
    font-size: 0.875rem;
    margin-bottom: 0.25rem;
    color: var(--secondary-color);
}

.filter-group select {
    width: 100%;
}

/* Buttons */
button {
    background-color: var(--accent-color);
    color: white;
    border: none;
    cursor: pointer;
    transition: background-color 0.2s;
}

button:hover {
    background-color: #2980b9;
}

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

button.secondary:hover {
    background-color: #2c3e50;
}

/* Result display */
.result {
    margin: 2rem 0;
    padding: 1.5rem;
    background-color: #f8f9fa;
    border-radius: var(--border-radius);
    text-align: center;
}

.exposure-display {
    font-size: 2rem;
    font-weight: bold;
    color: var(--primary-color);
    margin: 1rem 0;
}

.exposure-range {
    padding: 0.5rem;
    border-radius: var(--border-radius);
    font-size: 0.875rem;
    margin-top: 0.5rem;
}

.exposure-range.normal {
    background-color: var(--success-color);
    color: white;
}

.exposure-range.long {
    background-color: var(--warning-color);
    color: white;
}

.exposure-range.very-long {
    background-color: var(--error-color);
    color: white;
}

/* Instructions section */
.instructions {
    background-color: #f8f9fa;
    border-radius: var(--border-radius);
    margin-bottom: 2rem;
}

.instructions h2 {
    padding: 1rem;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.instructions h2::after {
    content: '▼';
    font-size: 0.8rem;
    transition: transform 0.3s;
}

.instructions.active h2::after {
    transform: rotate(180deg);
}

.instructions .content {
    padding: 0 1rem 1rem;
    display: none;
}

.instructions.active .content {
    display: block;
}

.instructions h3 {
    color: var(--secondary-color);
    margin: 1rem 0 0.5rem;
}

.instructions ul,
.instructions ol {
    padding-left: 1.5rem;
    margin-bottom: 1rem;
}

/* Footer */
footer {
    text-align: center;
    color: #666;
    font-size: 0.875rem;
    margin-top: 2rem;
}

/* Responsive adjustments */
@media (max-width: 600px) {
    .container {
        padding: var(--spacing-unit);
    }

    h1 {
        font-size: 1.5rem;
    }

    .exposure-display {
        font-size: 1.5rem;
    }

    .fstop-input-container {
        grid-template-columns: 1fr;
    }
}

/* Input validation styles */
input.error {
    border-color: var(--error-color);
}

.error-message {
    color: var(--error-color);
    font-size: 0.875rem;
    margin-top: 0.25rem;
}

/* Warning text */
.warning-text {
    margin-top: 1rem;
    padding: 0.75rem;
    border-radius: var(--border-radius);
    background-color: #fff3cd;
    border: 1px solid #ffeeba;
    color: #856404;
    font-size: 0.9rem;
    display: none;
}

.warning-text.visible {
    display: block;
}

/* Animation for updates */
@keyframes highlight {
    0% { background-color: var(--accent-color); color: white; }
    100% { background-color: transparent; color: var(--primary-color); }
}

.highlight {
    animation: highlight 1s ease-out;
}