Add theme: Arc Like Sidebar

themes/34fa17d3-3862-4126-b965-73e8914b6900/chrome.css

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+
+#main-window:-moz-window-inactive,
+#navigator-toolbox:-moz-window-inactive,
+#TabsToolbar:-moz-window-inactive,
+#tabbrowser-tabs:-moz-window-inactive,
+#tabs-newtab-button:-moz-window-inactive,
+#vertical-tabs-newtab-button:-moz-window-inactive,
+#zen-sidebar-bottom-buttons:-moz-window-inactive,
+#zen-workspaces-button:-moz-window-inactive {
+  opacity: 1 !important;
+  filter: none !important;
+}
+
+.tabbrowser-tab[selected]:-moz-window-inactive .tab-background,
+.tabbrowser-tab[visuallyselected]:-moz-window-inactive .tab-background {
+  background-image: none !important;
+  border: none !important;
+  outline: none !important;
+  opacity: 0.7 !important;
+}
+
+#tabbrowser-tabs .tabbrowser-tab,
+#tabbrowser-tabs .tabbrowser-tab .tab-label-container,
+#tabbrowser-tabs .tabbrowser-tab .tab-label,
+#tabbrowser-tabs .tabbrowser-tab .tab-text,
+.tabbrowser-tab .tab-label,
+.tabbrowser-tab .tab-text {
+  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", system-ui, sans-serif !important;
+  font-size: 14px !important;
+  font-weight: 450 !important;
+  letter-spacing: -0.01em !important;
+  -moz-osx-font-smoothing: auto !important;
+}

themes/34fa17d3-3862-4126-b965-73e8914b6900/readme.md

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+
+# Arc Like Sidebar
+
+Two small tweaks that make Zen's vertical sidebar feel closer to Arc on macOS:
+
+## 1. No fade when the window loses focus
+By default, Zen applies an opacity/filter to the sidebar and toolbar when the window is blurred, which makes tab text render really thin and washed out —
+almost unreadable at a glance. This mod removes that effect so your sidebar stays crisp and fully legible. The active tab pill is left slightly translucent
+(70%) as a subtle hint that the window isn't focused, similar to how Arc handles its unfocused state.
+
+## 2. Arc-like tab label rendering
+Bumps tab labels to system font (-apple-system / SF Pro Text), size 14px, weight 450, with native macOS font smoothing. The default Zen rendering looks
+noticeably thinner and smaller than Arc; this brings them in line.
+
+## What it doesn't touch
+- Border radius, colors, spacing, or layout.
+- Behavior when the window is focused (other than label font).
+- Non-macOS systems will still get the size/weight changes — the system font stack falls back gracefully.

themes/34fa17d3-3862-4126-b965-73e8914b6900/theme.json

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+{
+    "id": "34fa17d3-3862-4126-b965-73e8914b6900",
+    "name": "Arc Like Sidebar",
+    "description": "Arc-style sidebar: no fade when blurred + crisper tab font rendering.",
+    "homepage": "",
+    "style": "https://raw.githubusercontent.com/zen-browser/theme-store/main/themes/34fa17d3-3862-4126-b965-73e8914b6900/chrome.css",
+    "readme": "https://raw.githubusercontent.com/zen-browser/theme-store/main/themes/34fa17d3-3862-4126-b965-73e8914b6900/readme.md",
+    "image": "https://raw.githubusercontent.com/zen-browser/theme-store/main/themes/34fa17d3-3862-4126-b965-73e8914b6900/image.png",
+    "author": "simion",
+    "version": "1.0.0",
+    "tags": [],
+    "createdAt": "2026-05-18",
+    "updatedAt": "2026-05-18"
+}