govtechsg SGDS Theming Skill
How to customise the product theme — brand colours, day/night mode, and font — using SGDS CSS token overrides.
Prerequisites
Import themes/day.css before your custom CSS. See sgds-getting-started for the full import order.
Quick Decision Guide
| What you want to change | Token / mechanism |
|---|---|
| Product brand colour (custom) | Override --sgds-product-primary-{100–900} |
| Product brand colour (GovTech) | Import one themes/gt/<colour>.css + map to --sgds-product-primary-* |
| Enable dark/night mode | Import themes/night.css + add .sgds-night-theme to <html> |
| Font typeface | Override --sgds-font-family-brand |
Changing the Product Brand Colour
The default product colour is purple (--sgds-product-primary-*). Override the full 100–900 scale with your brand colour to retheme all primary UI elements at once.
Create a custom CSS file and override the primitive tokens in :root:
/* yourCustomCss.css */
:root {
--sgds-product-primary-100: #F5B6DA;
--sgds-product-primary-200: #F186C0;
--sgds-product-primary-300: #EE4FA6;
--sgds-product-primary-400: #EE0290;
--sgds-product-primary-500: #EF0078;
--sgds-product-primary-600: #DD0074;
--sgds-product-primary-700: #C6006E;
--sgds-product-primary-800: #B0006A;
--sgds-product-primary-900: #880061;
}
Import your custom CSS after the SGDS theme file so the overrides take effect:
import "@govtechsg/sgds-web-component/themes/day.css";
import "./yourCustomCss.css";
@import "@govtechsg/sgds-web-component/themes/day.css";
@import "./yourCustomCss.css";
The semantic tokens (--sgds-primary-*) reference the primitive scale, so changing the primitive values automatically flows through to all components that use the primary colour.
GovTech Brand Colours
GovTech products should use one of the pre-approved colour palettes in themes/gt/ rather than defining custom hex values. Each product picks exactly one colour — mixing multiple GT palettes is not allowed.
Available colours
| File | Colour |
|---|---|
themes/gt/blue.css |
Blue |
themes/gt/cyan.css |
Cyan |
themes/gt/magenta.css |
Magenta |
themes/gt/pink.css |
Pink |
themes/gt/purple.css |
Purple |
themes/gt/red.css |
Red |
How to apply
Each GT file defines --gt-color-100 through --gt-color-900 in :root. Map those onto the SGDS product primary scale in your custom CSS file:
/* yourCustomCss.css */
:root {
--sgds-product-primary-100: var(--gt-color-100);
--sgds-product-primary-200: var(--gt-color-200);
--sgds-product-primary-300: var(--gt-color-300);
--sgds-product-primary-400: var(--gt-color-400);
--sgds-product-primary-500: var(--gt-color-500);
--sgds-product-primary-600: var(--gt-color-600);
--sgds-product-primary-700: var(--gt-color-700);
--sgds-product-primary-800: var(--gt-color-800);
--sgds-product-primary-900: var(--gt-color-900);
}
Import order — the GT file must come before your custom CSS so the --gt-color-* variables are defined when the mapping runs:
import "@govtechsg/sgds-web-component/themes/day.css";
import "@govtechsg/sgds-web-component/themes/gt/blue.css"; // pick one colour only
import "./yourCustomCss.css";
@import "@govtechsg/sgds-web-component/themes/day.css";
@import "@govtechsg/sgds-web-component/themes/gt/blue.css"; /* pick one colour only */
@import "./yourCustomCss.css";
The same flow-through behaviour applies: changing --sgds-product-primary-* automatically updates all components that use the primary colour.
Day Mode (Default)
Day mode is the default. Importing themes/day.css is all that is needed — no extra configuration required.
@import "@govtechsg/sgds-web-component/themes/day.css";
Night Mode (Optional)
Night mode is opt-in. It is applied by adding the class sgds-night-theme to the <html> element, which activates the :root.sgds-night-theme selector defined in themes/night.css.
Setup
Import both theme files:
import "@govtechsg/sgds-web-component/themes/day.css";
import "@govtechsg/sgds-web-component/themes/night.css";
@import "@govtechsg/sgds-web-component/themes/day.css";
@import "@govtechsg/sgds-web-component/themes/night.css";
Activating night mode
Add the class to the <html> element to switch all tokens to their dark equivalents:
<html class="sgds-night-theme">
Toggle it at runtime via JavaScript:
document.documentElement.classList.toggle("sgds-night-theme");
How it works
themes/night.css redefines the same semantic tokens as themes/day.css but scoped to :root.sgds-night-theme. All SGDS components read from the same semantic tokens, so toggling the class switches the entire UI without changing any component markup.
Changing the Font
SGDS uses Inter by default via --sgds-font-family-brand. Override this token to use a different typeface:
:root {
--sgds-font-family-brand: "Your Font", system-ui, sans-serif;
}
You are responsible for loading the font assets — either via a <link> tag or @font-face. SGDS does not load custom fonts automatically. See sgds-getting-started for the optimised Inter Google Fonts URL if you are keeping the default font.
For AI Agents
- Always tell users to import their custom CSS after
themes/day.css— otherwise the override will be overwritten. - Brand colour overrides target primitive tokens (
--sgds-product-primary-{100–900}), not semantic tokens. Changing the primitives is the correct approach; do not override individual semantic tokens directly. - Night mode requires both the
themes/night.cssimport and thesgds-night-themeclass on<html>. Either alone is not enough. - Night mode is optional — only add
themes/night.csswhen the user explicitly needs dark mode support. - Day mode is always active by default; there is no
sgds-day-themeclass to add. - When overriding
--sgds-font-family-brand, remind the user to also load the font file themselves. - Custom overrides apply to both day and night mode simultaneously because they target
:root, which both theme selectors inherit from. - GovTech products must use a colour from
themes/gt/— not custom hex values. If a user is building a GovTech product and asks about brand colours, guide them to pick one GT colour and apply the--gt-color-*→--sgds-product-primary-*mapping pattern. Never let them import more than one GT colour file. - The GT colour file must be imported after
themes/day.cssand before the custom mapping CSS so that--gt-color-*variables are defined in time.