/* === Reset & Variables === */
*,
*::before,
*::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #21262d;
    --bg-input: #0d1117;
    --border: #30363d;
    --border-focus: #58a6ff;
    --text-primary: #e6edf3;
    --text-secondary: #8b949e;
    --text-muted: #6e7681;
    --accent: #58a6ff;
    --accent-hover: #79c0ff;
    --match-bg-1: rgba(255, 166, 0, 0.3);
    --match-border-1: #ffa600;
    --match-bg-2: rgba(0, 200, 150, 0.3);
    --match-border-2: #00c896;
    --match-bg-3: rgba(180, 100, 255, 0.3);
    --match-border-3: #b464ff;
    --match-bg-4: rgba(255, 80, 120, 0.3);
    --match-border-4: #ff5078;
    --error: #f85149;
    --success: #3fb950;
    --radius: 8px;
    --radius-sm: 4px;
    --font-mono: 'Cascadia Code', 'Fira Code', 'JetBrains Mono', 'Consolas', monospace;
    --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif;
    --shadow: 0 2px 8px rgba(0, 0, 0, 0.3);
}

html {
    font-size: 15px;
}

body {
    font-family: var(--font-sans);
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.5;
}

/* === Header === */
header {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    padding: 0.75rem 1.5rem;
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
}

h1 {
    font-size: 1.25rem;
    font-weight: 700;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.logo-icon {
    font-family: var(--font-mono);
    color: var(--accent);
    font-size: 1.1rem;
}

.header-actions {
    display: flex;
    gap: 0.5rem;
}

.header-actions button {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    padding: 0.4rem 0.75rem;
    background: var(--bg-tertiary);
    color: var(--text-primary);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.8rem;
    transition: all 0.15s;
}

.header-actions button:hover {
    background: var(--border);
    border-color: var(--text-muted);
}

/* === Main Layout === */
main {
    max-width: 1400px;
    margin: 0 auto;
    padding: 1.5rem;
}

.app-layout {
    display: flex;
    gap: 1.5rem;
    align-items: flex-start;
}

.editor-panel {
    flex: 1;
    min-width: 0;
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

/* === Sections === */
section {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1rem;
}

label {
    display: block;
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
}

/* === Regex Input === */
.regex-row {
    display: flex;
    align-items: center;
    gap: 0;
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 0 0.5rem;
    transition: border-color 0.15s;
}

.regex-row:focus-within {
    border-color: var(--border-focus);
}

.regex-delimiter {
    font-family: var(--font-mono);
    font-size: 1.1rem;
    color: var(--accent);
    user-select: none;
    padding: 0 0.15rem;
}

#regexInput {
    flex: 1;
    background: transparent;
    border: none;
    color: var(--text-primary);
    font-family: var(--font-mono);
    font-size: 0.95rem;
    padding: 0.6rem 0.4rem;
    outline: none;
    min-width: 0;
}

#regexInput::placeholder {
    color: var(--text-muted);
}

.flags-container {
    display: flex;
    gap: 0.15rem;
    padding: 0 0.25rem;
    border-left: 1px solid var(--border);
    margin-left: 0.25rem;
}

.flag-toggle {
    display: flex;
    align-items: center;
    margin: 0;
}

.flag-toggle input {
    display: none;
}

.flag-toggle span {
    display: block;
    padding: 0.25rem 0.4rem;
    font-family: var(--font-mono);
    font-size: 0.8rem;
    color: var(--text-muted);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all 0.15s;
    user-select: none;
}

.flag-toggle input:checked + span {
    color: var(--accent);
    background: rgba(88, 166, 255, 0.15);
}

.flag-toggle span:hover {
    color: var(--text-primary);
}

#copyRegexBtn {
    background: transparent;
    border: none;
    color: var(--text-muted);
    cursor: pointer;
    padding: 0.4rem;
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    transition: color 0.15s;
}

#copyRegexBtn:hover {
    color: var(--text-primary);
}

.error-message {
    color: var(--error);
    font-size: 0.8rem;
    margin-top: 0.4rem;
    font-family: var(--font-mono);
    min-height: 0;
    overflow: hidden;
    transition: all 0.15s;
}

.error-message:empty {
    display: none;
}

/* === Mode Toggle === */
.mode-section {
    padding: 0.5rem 1rem;
}

.mode-toggle {
    display: flex;
    gap: 0;
    background: var(--bg-input);
    border-radius: var(--radius-sm);
    border: 1px solid var(--border);
    overflow: hidden;
    width: fit-content;
}

.mode-btn {
    padding: 0.4rem 1.25rem;
    background: transparent;
    border: none;
    color: var(--text-secondary);
    font-size: 0.8rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.15s;
}

.mode-btn.active {
    background: var(--accent);
    color: #fff;
}

.mode-btn:hover:not(.active) {
    color: var(--text-primary);
    background: var(--bg-tertiary);
}

/* === Test String === */
.test-string-wrapper {
    position: relative;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    overflow: hidden;
}

.test-string-wrapper:focus-within {
    border-color: var(--border-focus);
}

.highlight-overlay {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    padding: 0.75rem;
    font-family: var(--font-mono);
    font-size: 0.9rem;
    line-height: 1.6;
    white-space: pre-wrap;
    word-wrap: break-word;
    overflow: auto;
    pointer-events: none;
    color: transparent;
}

.highlight-overlay mark {
    background: var(--match-bg-1);
    border-bottom: 2px solid var(--match-border-1);
    color: transparent;
    border-radius: 2px;
}

.highlight-overlay mark.match-color-0 {
    background: var(--match-bg-1);
    border-bottom-color: var(--match-border-1);
}

.highlight-overlay mark.match-color-1 {
    background: var(--match-bg-2);
    border-bottom-color: var(--match-border-2);
}

.highlight-overlay mark.match-color-2 {
    background: var(--match-bg-3);
    border-bottom-color: var(--match-border-3);
}

.highlight-overlay mark.match-color-3 {
    background: var(--match-bg-4);
    border-bottom-color: var(--match-border-4);
}

#testString {
    width: 100%;
    min-height: 160px;
    background: var(--bg-input);
    color: var(--text-primary);
    border: none;
    padding: 0.75rem;
    font-family: var(--font-mono);
    font-size: 0.9rem;
    line-height: 1.6;
    resize: vertical;
    outline: none;
    position: relative;
    z-index: 1;
    caret-color: var(--text-primary);
}

#testString::placeholder {
    color: var(--text-muted);
}

/* Transparent background to show highlights */
#testString:not(:placeholder-shown) {
    background: transparent;
}

/* === Replace Section === */
.replace-section {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.replace-section.hidden {
    display: none;
}

#replaceInput {
    width: 100%;
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-family: var(--font-mono);
    font-size: 0.9rem;
    padding: 0.6rem 0.75rem;
    outline: none;
    transition: border-color 0.15s;
}

#replaceInput:focus {
    border-color: var(--border-focus);
}

.replace-result {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 0.75rem;
    font-family: var(--font-mono);
    font-size: 0.9rem;
    line-height: 1.6;
    min-height: 60px;
    white-space: pre-wrap;
    word-wrap: break-word;
    color: var(--text-secondary);
}

/* === Explanation === */
.explanation-section h3 {
    font-size: 0.85rem;
    margin-bottom: 0.5rem;
    color: var(--text-secondary);
}

.explanation-content {
    font-size: 0.85rem;
    line-height: 1.7;
}

.explanation-content .token {
    display: inline-flex;
    align-items: center;
    gap: 0.3rem;
    margin: 0.15rem 0.1rem;
    padding: 0.15rem 0.45rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    font-family: var(--font-mono);
    font-size: 0.8rem;
}

.explanation-content .token-pattern {
    color: var(--accent);
    font-weight: 600;
}

.explanation-content .token-desc {
    color: var(--text-secondary);
    font-family: var(--font-sans);
    font-size: 0.75rem;
}

.placeholder-text {
    color: var(--text-muted);
    font-style: italic;
    font-size: 0.85rem;
}

/* === Match Results === */
.results-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 0.5rem;
}

.results-header h3 {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.match-count {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--accent);
    background: rgba(88, 166, 255, 0.1);
    padding: 0.2rem 0.6rem;
    border-radius: 999px;
}

.match-results {
    max-height: 400px;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
}

.match-item {
    display: flex;
    align-items: flex-start;
    gap: 0.75rem;
    padding: 0.5rem 0.6rem;
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
    border-left: 3px solid var(--match-border-1);
    font-size: 0.8rem;
}

.match-item.match-color-0 { border-left-color: var(--match-border-1); }
.match-item.match-color-1 { border-left-color: var(--match-border-2); }
.match-item.match-color-2 { border-left-color: var(--match-border-3); }
.match-item.match-color-3 { border-left-color: var(--match-border-4); }

.match-index {
    font-family: var(--font-mono);
    color: var(--text-muted);
    font-size: 0.7rem;
    min-width: 2rem;
    padding-top: 0.1rem;
}

.match-value {
    font-family: var(--font-mono);
    color: var(--text-primary);
    word-break: break-all;
    flex: 1;
}

.match-meta {
    font-size: 0.7rem;
    color: var(--text-muted);
    white-space: nowrap;
}

.match-groups {
    font-size: 0.7rem;
    color: var(--text-secondary);
    margin-top: 0.2rem;
}

.match-groups span {
    display: inline-block;
    margin-right: 0.5rem;
    padding: 0.1rem 0.3rem;
    background: var(--bg-secondary);
    border-radius: 2px;
}

/* === Cheat Sheet Sidebar === */
.cheat-sheet {
    width: 320px;
    min-width: 280px;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    position: sticky;
    top: 4.5rem;
    max-height: calc(100vh - 6rem);
    overflow-y: auto;
    display: none;
}

.cheat-sheet.visible {
    display: block;
}

.cheat-sheet-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.75rem 1rem;
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    background: var(--bg-secondary);
    z-index: 1;
}

.cheat-sheet-header h2 {
    font-size: 0.9rem;
}

.close-btn {
    background: transparent;
    border: none;
    color: var(--text-muted);
    font-size: 1.3rem;
    cursor: pointer;
    padding: 0.2rem;
    line-height: 1;
}

.close-btn:hover {
    color: var(--text-primary);
}

.cheat-sheet-content {
    padding: 0.75rem 1rem;
}

.cheat-category {
    margin-bottom: 1rem;
}

.cheat-category h4 {
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--text-muted);
    margin-bottom: 0.4rem;
    padding-bottom: 0.25rem;
    border-bottom: 1px solid var(--border);
}

.cheat-item {
    display: flex;
    align-items: baseline;
    gap: 0.5rem;
    padding: 0.2rem 0;
    font-size: 0.78rem;
    color: var(--text-secondary);
}

.cheat-item code {
    font-family: var(--font-mono);
    color: var(--accent);
    background: var(--bg-tertiary);
    padding: 0.1rem 0.35rem;
    border-radius: 3px;
    font-size: 0.75rem;
    min-width: 3.5rem;
    text-align: center;
    flex-shrink: 0;
}

.cheat-item.clickable {
    cursor: pointer;
    border-radius: var(--radius-sm);
    padding: 0.3rem 0.25rem;
    transition: background 0.15s;
}

.cheat-item.clickable:hover {
    background: var(--bg-tertiary);
}

/* === Toast === */
.toast {
    position: fixed;
    bottom: 1.5rem;
    left: 50%;
    transform: translateX(-50%) translateY(100%);
    background: var(--bg-tertiary);
    color: var(--text-primary);
    padding: 0.5rem 1.25rem;
    border-radius: var(--radius);
    border: 1px solid var(--border);
    font-size: 0.8rem;
    opacity: 0;
    transition: all 0.3s ease;
    z-index: 1000;
    pointer-events: none;
}

.toast.show {
    opacity: 1;
    transform: translateX(-50%) translateY(0);
}

/* === Footer === */
footer {
    text-align: center;
    padding: 1.5rem;
    color: var(--text-muted);
    font-size: 0.78rem;
    border-top: 1px solid var(--border);
    margin-top: 2rem;
}

footer a {
    color: var(--accent);
    text-decoration: none;
}

footer a:hover {
    text-decoration: underline;
}

/* === Scrollbar === */
::-webkit-scrollbar {
    width: 6px;
    height: 6px;
}

::-webkit-scrollbar-track {
    background: transparent;
}

::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 3px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* === Responsive === */
@media (max-width: 900px) {
    .cheat-sheet {
        position: fixed;
        top: 0;
        right: 0;
        bottom: 0;
        width: 300px;
        max-height: 100vh;
        border-radius: 0;
        z-index: 200;
        box-shadow: -4px 0 20px rgba(0, 0, 0, 0.5);
    }

    main {
        padding: 1rem;
    }
}

@media (max-width: 600px) {
    header {
        padding: 0.5rem 1rem;
    }

    .header-content {
        flex-wrap: wrap;
    }

    h1 {
        font-size: 1.05rem;
    }

    .header-actions button span {
        display: none;
    }

    .flags-container {
        gap: 0;
    }

    .flag-toggle span {
        padding: 0.2rem 0.3rem;
        font-size: 0.75rem;
    }

    main {
        padding: 0.75rem;
    }

    section {
        padding: 0.75rem;
    }

    .cheat-sheet {
        width: 85vw;
    }

    .match-item {
        flex-direction: column;
        gap: 0.25rem;
    }
}