:root {
    --bg-color: #0f1419;
    --surface-color: #1a2028;
    --surface-elevated: #232b36;
    --text-primary: #e6edf3;
    --text-secondary: #8b95a1;
    --accent-color: #58a6ff;
    --accent-hover: #79b8ff;
    --border-color: #2d333b;
    --strength-weak: #f85149;
    --strength-medium: #d29922;
    --strength-strong: #3fb950;
    --strength-excellent: #58a6ff;
    --font-mono: 'SFMono-Regular', Consolas, 'Liberation Mono', Menlo, monospace;
    --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
}

@media (prefers-color-scheme: light) {
    :root {
        --bg-color: #f6f8fa;
        --surface-color: #ffffff;
        --surface-elevated: #f0f3f6;
        --text-primary: #1f2328;
        --text-secondary: #59636e;
        --accent-color: #0969da;
        --accent-hover: #0860c9;
        --border-color: #d1d9e0;
    }
}

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

body {
    font-family: var(--font-sans);
    background-color: var(--bg-color);
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 1rem;
    line-height: 1.5;
}

.container {
    background-color: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 2rem;
    width: 100%;
    max-width: 560px;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.15);
}

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

h1 {
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.subtitle {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    border: 0;
}

.output-section {
    margin-bottom: 2rem;
}

.password-display {
    display: flex;
    align-items: stretch;
    background-color: var(--surface-elevated);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    overflow: hidden;
    margin-bottom: 0.75rem;
}

#password-output {
    flex: 1;
    padding: 1rem;
    font-family: var(--font-mono);
    font-size: 1rem;
    word-break: break-all;
    user-select: all;
    color: var(--text-primary);
    min-height: 3rem;
    display: flex;
    align-items: center;
}

#password-output:empty::before {
    content: "Click Generate to create a password";
    color: var(--text-secondary);
}

.copy-button {
    background-color: transparent;
    border: none;
    border-left: 1px solid var(--border-color);
    color: var(--accent-color);
    padding: 0 1.25rem;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.15s ease;
    font-family: inherit;
    font-size: 0.9rem;
}

.copy-button:hover:not(:disabled) {
    background-color: var(--border-color);
}

.copy-button:disabled {
    color: var(--text-secondary);
    cursor: not-allowed;
}

.copy-button.copied {
    color: var(--strength-strong);
}

.strength-meter {
    height: 6px;
    background-color: var(--surface-elevated);
    border-radius: 3px;
    overflow: hidden;
    margin-bottom: 0.5rem;
}

.strength-bar {
    height: 100%;
    width: 0%;
    background-color: var(--strength-weak);
    transition: width 0.3s ease, background-color 0.3s ease;
}

.strength-bar.weak { background-color: var(--strength-weak); width: 25%; }
.strength-bar.medium { background-color: var(--strength-medium); width: 50%; }
.strength-bar.strong { background-color: var(--strength-strong); width: 75%; }
.strength-bar.excellent { background-color: var(--strength-excellent); width: 100%; }

.strength-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    min-height: 1.25rem;
}

.controls {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.control-group {
    border: none;
}

.control-group > label,
.control-group > legend {
    display: block;
    font-weight: 600;
    margin-bottom: 0.75rem;
    color: var(--text-primary);
    font-size: 0.95rem;
}

.length-control {
    display: flex;
    align-items: center;
    gap: 1rem;
}

#length-slider {
    flex: 1;
    height: 6px;
    -webkit-appearance: none;
    appearance: none;
    background: var(--surface-elevated);
    border-radius: 3px;
    outline: none;
    cursor: pointer;
}

#length-slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 18px;
    height: 18px;
    background: var(--accent-color);
    border-radius: 50%;
    cursor: pointer;
    transition: background-color 0.15s ease;
}

#length-slider::-webkit-slider-thumb:hover {
    background: var(--accent-hover);
}

#length-slider::-moz-range-thumb {
    width: 18px;
    height: 18px;
    background: var(--accent-color);
    border-radius: 50%;
    cursor: pointer;
    border: none;
}

#length-input {
    width: 4.5rem;
    padding: 0.5rem;
    background-color: var(--surface-elevated);
    border: 1px solid var(--border-color);
    border-radius: 6px;
    color: var(--text-primary);
    font-family: var(--font-mono);
    font-size: 0.95rem;
    text-align: center;
}

#length-input:focus {
    outline: 2px solid var(--accent-color);
    outline-offset: 1px;
    border-color: var(--accent-color);
}

.checkbox-label {
    display: flex;
    align-items: center;
    gap: 0.625rem;
    padding: 0.375rem 0;
    cursor: pointer;
    font-size: 0.9rem;
    color: var(--text-primary);
    font-weight: normal;
    margin-bottom: 0;
}

.checkbox-label input[type="checkbox"] {
    width: 1.1rem;
    height: 1.1rem;
    cursor: pointer;
    accent-color: var(--accent-color);
}

.generate-button {
    background-color: var(--accent-color);
    color: white;
    border: none;
    padding: 0.875rem 1.5rem;
    font-size: 1rem;
    font-weight: 600;
    border-radius: 8px;
    cursor: pointer;
    transition: background-color 0.15s ease, transform 0.05s ease;
    font-family: inherit;
}

.generate-button:hover {
    background-color: var(--accent-hover);
}

.generate-button:active {
    transform: scale(0.98);
}

.generate-button:focus-visible {
    outline: 2px solid var(--accent-hover);
    outline-offset: 2px;
}

footer {
    margin-top: 2rem;
    text-align: center;
    color: var(--text-secondary);
    font-size: 0.8rem;
}

@media (max-width: 480px) {
    .container {
        padding: 1.5rem;
    }

    h1 {
        font-size: 1.4rem;
    }

    .length-control {
        flex-wrap: wrap;
    }
}