:root {
    --primary: #2496ED;
    --primary-hover: #1b7bc4;
    --secondary: #66B2FF;
    --accent: #FDCB6E;
    --bg-main: #0A1219;
    --bg-pane: #111D28;
    --bg-pane-alt: #172635;
    --text-main: #FFFFFF;
    --text-muted: #94A3B8;
    --border: #2A3B4D;
    --danger: #EF4444;
    --success: #22C55E;

    --radius: 12px;
    --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
    --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
}

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

body {
    font-family: var(--font-sans);
    background-color: var(--bg-main);
    color: var(--text-main);
    height: 100vh;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

/* Header */
.app-header {
    background-color: var(--bg-pane);
    border-bottom: 1px solid var(--border);
    padding: 0 20px;
    height: 60px;
    flex-shrink: 0;
}

.header-content {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 100%;
}

.logo {
    display: flex;
    align-items: center;
    gap: 12px;
    color: var(--primary);
}

.logo svg {
    width: 28px;
    height: 28px;
}

.logo h1 {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-main);
    letter-spacing: -0.02em;
}

.actions {
    display: flex;
    gap: 12px;
}

/* Buttons */
.btn {
    padding: 8px 16px;
    border-radius: 8px;
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
    border: none;
    font-family: inherit;
    text-decoration: none;
    display: inline-flex;
    align-items: center;
    justify-content: center;
}

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

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

.btn-secondary {
    background-color: var(--bg-pane-alt);
    color: var(--text-main);
    border: 1px solid var(--border);
}

.btn-secondary:hover {
    background-color: #1e3347;
}

.btn-icon {
    background: none;
    border: none;
    color: var(--text-muted);
    cursor: pointer;
    padding: 4px;
    border-radius: 4px;
}

.btn-icon:hover {
    color: var(--text-main);
    background: var(--bg-pane-alt);
}

/* Layout */
.split-pane {
    display: flex;
    flex: 1;
    overflow: hidden;
    height: calc(100vh - 60px);
}

.pane {
    flex: 1;
    display: flex;
    flex-direction: column;
    min-width: 0;
}

.editor-pane {
    border-right: 1px solid var(--border);
}

.pane-header {
    padding: 12px 20px;
    background-color: var(--bg-pane);
    border-bottom: 1px solid var(--border);
    display: flex;
    align-items: center;
    gap: 16px;
    flex-shrink: 0;
}

.pane-header h2 {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* Editor */
.editor-container {
    flex: 1;
    padding: 0;
    position: relative;
}

textarea#html-input {
    width: 100%;
    height: 100%;
    background-color: var(--bg-main);
    color: #e2e8f0;
    border: none;
    padding: 20px;
    font-family: var(--font-mono);
    font-size: 0.875rem;
    line-height: 1.6;
    resize: none;
    outline: none;
}

/* Preview pane controls */
.preview-controls {
    justify-content: space-between;
    flex-wrap: wrap;
}

.view-toggles {
    display: flex;
    background-color: var(--bg-pane-alt);
    border-radius: 6px;
    padding: 2px;
}

.btn-toggle {
    background: transparent;
    border: none;
    color: var(--text-muted);
    padding: 6px 12px;
    border-radius: 4px;
    font-size: 0.8125rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
}

.btn-toggle.active {
    background-color: var(--primary);
    color: white;
}

.client-options {
    display: flex;
    align-items: center;
    gap: 16px;
}

.dropdown {
    background-color: var(--bg-pane-alt);
    color: var(--text-main);
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 6px 12px;
    font-size: 0.8125rem;
    outline: none;
}

/* Toggle Switch */
.toggle-switch {
    display: flex;
    align-items: center;
    gap: 8px;
    cursor: pointer;
    font-size: 0.8125rem;
    color: var(--text-muted);
}

.toggle-switch input {
    display: none;
}

.toggle-switch .slider {
    width: 32px;
    height: 18px;
    background-color: var(--bg-pane-alt);
    border: 1px solid var(--border);
    border-radius: 9px;
    position: relative;
    transition: 0.2s;
}

.toggle-switch .slider::before {
    content: '';
    position: absolute;
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background-color: var(--text-muted);
    top: 2px;
    left: 3px;
    transition: 0.2s;
}

.toggle-switch input:checked+.slider {
    background-color: var(--primary);
    border-color: var(--primary);
}

.toggle-switch input:checked+.slider::before {
    transform: translateX(13px);
    background-color: white;
}

/* Slider */
.width-slider-wrap {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 0.8125rem;
    color: var(--text-muted);
}

.width-slider-wrap input[type=range] {
    accent-color: var(--primary);
}

/* Preview Area */
.preview-container {
    flex: 1;
    background-color: #1e293b;
    /* Desktop-like background behind email */
    overflow-y: auto;
    padding: 20px;
    display: flex;
    justify-content: center;
    position: relative;
}

.preview-wrapper {
    width: 100%;
    background-color: white;
    /* Default email bg */
    border-radius: var(--radius);
    overflow: hidden;
    box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.5);
    transition: max-width 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    flex-direction: column;
}

#preview-iframe {
    width: 100%;
    height: 100%;
    min-height: 500px;
    border: none;
    background-color: transparent;
}

.text-preview {
    padding: 40px;
    color: #333;
    background: #f8fafc;
    font-family: var(--font-mono);
    font-size: 0.875rem;
    line-height: 1.7;
    white-space: pre-wrap;
    min-height: 500px;
}

/* Client Specific Constraints (Simulated limits) */
.client-gmail img {
    max-width: 100% !important;
}

.client-outlook {
    font-family: Calibri, sans-serif !important;
}

.client-apple {
    -webkit-text-size-adjust: none;
}

/* Overlays & Badges */
.warning-badge {
    background-color: rgba(245, 158, 11, 0.2);
    color: var(--accent);
    padding: 2px 8px;
    border-radius: 4px;
    font-size: 0.75rem;
    border: 1px solid rgba(245, 158, 11, 0.3);
}

.hidden {
    display: none !important;
}

.overlay-panel {
    position: absolute;
    top: 20px;
    right: 20px;
    width: 320px;
    max-height: calc(100% - 40px);
    background: var(--bg-pane);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.8);
    display: flex;
    flex-direction: column;
    z-index: 10;
}

.overlay-panel .panel-header {
    padding: 12px 16px;
    border-bottom: 1px solid var(--border);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.overlay-panel .panel-header h3 {
    font-size: 0.875rem;
    color: var(--text-main);
}

.overlay-panel .panel-content {
    padding: 16px;
    overflow-y: auto;
    font-size: 0.8125rem;
    color: var(--text-muted);
}

.a11y-item {
    margin-bottom: 12px;
    padding: 10px;
    background: var(--bg-pane-alt);
    border-radius: 6px;
    border-left: 3px solid var(--danger);
}

.a11y-item.pass {
    border-left-color: var(--success);
}