.app-header {
    display: grid;
    grid-template-columns: minmax(240px, 1.1fr) minmax(220px, 1fr) auto;
    gap: var(--space-5);
    align-items: center;
    padding: var(--space-5) var(--space-6);
    background: var(--surface-elevated);
    border-radius: var(--radius-lg);
    border: 1px solid var(--stroke);
    box-shadow: var(--shadow-md);
    backdrop-filter: blur(20px);
}

.brand {
    display: flex;
    align-items: center;
    gap: var(--space-4);
}

.brand-copy {
    display: flex;
    flex-direction: column;
    gap: var(--space-1);
}

.brand-mark {
    width: 54px;
    height: 54px;
    border-radius: 18px;
    background: var(--accent);
    color: #fff;
    display: grid;
    place-items: center;
    font-family: var(--font-display);
    font-size: 1.6rem;
    box-shadow: 0 12px 24px rgba(27, 127, 121, 0.2);
}

.brand-title {
    font-family: var(--font-display);
    font-size: 1.6rem;
    letter-spacing: 0.5px;
}

.brand-subtitle {
    color: var(--ink-muted);
    font-size: 0.95rem;
    max-width: 420px;
}

.brand-tags {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-2);
}

.header-actions {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    justify-content: flex-end;
    flex-wrap: wrap;
}

.workspace {
    display: flex;
    align-items: stretch;
    gap: 0;
}

.panel {
    background: var(--surface-elevated);
    border-radius: var(--radius-lg);
    border: 1px solid var(--stroke);
    box-shadow: var(--shadow-sm);
    padding: var(--space-5);
    display: flex;
    flex-direction: column;
    gap: var(--space-4);
    position: relative;
    min-height: 540px;
}

.editor-panel,
.preview-panel {
    flex: 1 1 0;
    min-width: var(--panel-min-width);
}

.panel-heading {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--space-4);
}

.panel-heading h2 {
    font-family: var(--font-display);
    font-size: 1.4rem;
    margin-bottom: var(--space-1);
}

.panel-heading p {
    color: var(--ink-muted);
    font-size: 0.9rem;
}

.toolbar {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-2);
    padding: var(--space-3);
    border-radius: var(--radius-md);
    background: rgba(255, 255, 255, 0.7);
    border: 1px solid var(--stroke);
}

#monaco-container {
    flex: 1;
    min-height: 360px;
    border-radius: var(--radius-md);
    overflow: hidden;
    border: 1px solid var(--stroke);
    box-shadow: inset 0 0 0 1px rgba(15, 23, 42, 0.04);
}

.fallback-input {
    display: none;
    min-height: 360px;
    padding: var(--space-4);
    border-radius: var(--radius-md);
    border: 1px solid var(--stroke);
    background: #fff;
    color: var(--ink);
    font-family: var(--font-mono);
    line-height: 1.6;
    resize: vertical;
}

.status-bar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--space-4);
    color: var(--ink-soft);
    font-size: 0.85rem;
}

.stats {
    display: flex;
    gap: var(--space-3);
    flex-wrap: wrap;
}

.status-meta {
    font-size: 0.85rem;
}

.preview-panel {
    overflow: hidden;
}

.preview-meta {
    color: var(--ink-soft);
    font-size: 0.85rem;
}

.splitter {
    flex: 0 0 12px;
    cursor: col-resize;
    position: relative;
    align-self: stretch;
    touch-action: none;
}

.splitter::before {
    content: "";
    position: absolute;
    top: var(--space-5);
    bottom: var(--space-5);
    left: 50%;
    width: 2px;
    background: var(--stroke-strong);
    border-radius: 999px;
    transform: translateX(-50%);
    transition: background var(--transition);
}

.splitter:hover::before {
    background: var(--accent);
}

.resizing,
.resizing * {
    cursor: col-resize;
    user-select: none;
}

.scroll-indicator {
    position: absolute;
    top: var(--space-5);
    right: var(--space-5);
    width: 5px;
    height: calc(100% - 100px);
    background: rgba(27, 127, 121, 0.15);
    border-radius: 999px;
    z-index: 3;
}

.scroll-thumb {
    width: 100%;
    background: var(--accent);
    border-radius: 999px;
    transition: height 0.2s ease;
}

.app-footer {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--space-4);
    padding: var(--space-4) var(--space-5);
    border-radius: var(--radius-lg);
    border: 1px solid var(--stroke);
    background: rgba(255, 255, 255, 0.75);
    backdrop-filter: blur(18px);
}

.footer-actions {
    display: flex;
    align-items: center;
    gap: var(--space-3);
}

.footer-note {
    color: var(--ink-muted);
    font-size: 0.9rem;
}

.preview-hidden .workspace {
    gap: 0;
}

.preview-hidden #preview-panel {
    display: none;
}

.preview-hidden .splitter {
    display: none;
}

.fallback-mode #monaco-container {
    display: none;
}

.fallback-mode .fallback-input {
    display: block;
}

@media (max-width: 1100px) {
    .app-header {
        grid-template-columns: 1fr;
        text-align: left;
    }

    .header-actions {
        justify-content: flex-start;
    }
}

@media (max-width: 900px) {
    .workspace {
        flex-direction: column;
        gap: var(--space-4);
    }

    .panel {
        min-height: 480px;
    }

    .editor-panel,
    .preview-panel {
        min-width: auto;
    }

    .splitter {
        display: none;
    }

    .scroll-indicator {
        display: none;
    }
}

@media (max-width: 640px) {
    body {
        padding: var(--space-4);
    }

    .app-header {
        padding: var(--space-4);
    }

    .panel {
        padding: var(--space-4);
    }

    .toolbar {
        padding: var(--space-2);
    }
}