Changing a diagram's look is a matter of picking a new theme and watching the canvas update. livediagram brings the theme picker front and centre in a dedicated dialog, with the same category browse you see when starting a new diagram, so there is plenty of room to compare looks.
Opening the dialog
Right-click an empty patch of canvas and choose Change Theme. This opens the Tab Appearance dialog on its Theme tab. The dialog also has a Canvas tab for the backdrop pattern and colours, and you can switch between the two from the tab strip below the header. The same controls also live in the floating palette, but the dialog gives them more room.
The dialog is an editor, not a wizard: there is no Apply or Cancel. Every change applies live to the active tab, and closing it (with the X, the Escape key, or a click on the backdrop) simply dismisses it without rolling anything back.
Browsing by category
The Theme tab opens on an overview: a Basic quick-pick plus a card for each category, such as Cool, Warm, Dark, Multi-colour, and Formal, alongside a Custom category for your own saved themes. Click a category to drill into its themes, with an "All themes" affordance to step back out.
Right-click the canvas and choose Change Theme to open the dialog on the Theme tab.
Pick a category, then click a theme to apply it live. Double-click a theme to apply it and close the dialog in one move.
Recolouring elements
Applying a theme keeps colours you have hand-set on individual shapes and text, so deliberate customisations survive the switch. Arrows are the one exception: every arrow's stroke always snaps to the new theme's colour, because connectors left on an old hue read as broken. If you want a clean slate, the Reset elements to theme action repaints every element on the tab to the new theme's defaults, overriding your customisations.
Use double-click to apply and close once you have found the theme you want, and single clicks while you are still comparing options.
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