Theme Editor
Repaint the IDE from inside itself — and the one rule about what sticks when you leave.
Most editors let you pick a theme from a list. Semantix lets you open the running app, point at any part of it, and change how it looks — while you keep using it.
The Theme Editor is a mode, not a settings page. The IDE stays fully visible and fully working underneath; you are editing the thing you are looking at.
Opening it#
Menu bar → User → Theme Editor.
The same item closes it again. There is no keyboard shortcut and no toolbar button — that one menu item is the door. The mode is not remembered: every restart begins in normal coding mode.
While it is open you'll see a pill at the top of the screen reading UI Edit Mode, with a pulsing red dot and the word Esc. Clicking the pill leaves. So does pressing Escape.
Important
Escape leaves the editor from almost anywhere. An open colour picker swallows it properly, so Escape there just closes the picker. Everywhere else it exits — including places that look like they should cancel something smaller: the colour sampler and the window-selection lasso both treat Escape as "cancel this" and let the editor's own handler fire, so you drop out entirely.
The one that catches people: pressing Escape while typing in the Ask Claude box exits the editor and clears the conversation. Use the tool buttons rather than Escape.
One thing changes while you're in the mode: the 3D graph suspends. The centre of the IDE goes quiet so the GPU belongs to the editor, and the graph comes back when you leave. Nothing is lost.
The two ways to target something#
There are two editors inside the Theme Editor, and they are genuinely different tools. Reaching for the wrong one is the most common way to be confused here.
The Sections map — a small wireframe of the IDE. Click a region, drill into its parts, and edit that part. You are writing a rule, so it applies to every element the part covers: style Row and every row in the file tree changes. This is how you theme the app. → Sections and parts
The element inspector — pick the Material Inspector tool and click any element in the live UI. You are editing that one element. This is how you fix a single thing that a rule can't reach. → Styling one element
Above both sits the whole-app layer: the theme itself, its colours, fonts and tokens. → Themes and colours
⚑ What sticks when you leave#
This is the one rule to learn before you spend an hour in here, because the editor holds three different kinds of change with three different lifespans and tells you which is which nowhere.
| What you changed | What happens when you leave |
|---|---|
| Theme colours, fonts, syntax colours, wallpaper | Reverts — unless you saved |
| Part edits, and edits to a paintable surface | Sticks. No save needed, survives a restart |
| Custom classes on an element | Gone. Never saved at all |
Entering the mode takes a snapshot of your colours and fonts. Leaving restores it. So an afternoon of nudging the accent colour vanishes on Escape unless you press Save — while the gradient you painted onto the header in the Sections map is already permanent, no save involved.
Important
Picking a theme commits, even though editing does not. If you switch themes mid-session, that switch is kept when you leave. The reasoning is that a theme is one click to switch back, so choosing one counts as deciding.
Switching is a clean switch, and it takes more with it than the colours: your unsaved colour edits and your part edits are discarded the moment you pick a different theme, replaced by whatever the incoming theme bakes in — usually nothing. Painted surfaces are the exception and follow you across. The unsaved-edits dot beside the theme name is the only warning you get.
Save before switching if you want to keep any of it.
Saving, and the save bar#
The bar at the top — beside the status pill — is always available, so you never have to go looking for a panel to keep your work. It holds the theme dropdown, the unsaved-edits dot, a name box with Save, Update, Ask, and icon buttons for export, share card and import. A delete button joins them once you're on a theme of your own; built-ins can't be deleted, so on a fresh install it isn't there.
Built-in themes cannot be overwritten. Editing one and pressing save writes a new theme instead.
→ Saving, sharing and the share card
The rest of these pages#
- Themes and colours — the four shipped themes, and the panel where you change colours, syntax highlighting, fonts and window translucency.
- Sections and parts — the six regions of the IDE and the parts inside them.
- Styling one element — the inspector, its property controls, and the raw CSS escape hatches.
- Gradients — the gradient brush: types, stops, animation, and where a gradient can be painted.
- Saving, sharing and the share card — keeping a look, moving it between machines, and the poster it can draw of itself.
- Ask Claude for a theme — describe a look in words and watch the IDE repaint as the answer arrives.