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← DOM Manipulation with JavaScript
○The page is a tree○Exercise: follow the document reference○Load a script when the page is ready○Exercise: initialize a deferred script○Find one element by id or CSS selector○Exercise: select a notice and label○Compare DOM properties, HTML attributes, and node types○Exercise: inspect a room input and its nodes✦Module Quiz
○Find every match with querySelectorAll○Exercise: label every trail stop○Move from a child to its relatives○Exercise: trace a nested card○Check for missing elements and search within a card○Exercise: update only the chosen card○Compare a live HTMLCollection with a static NodeList○Exercise: safely expand a live collection✦Module Quiz
○Safe text and HTML○Exercise: render a safe notice○Read and change link attributes○Exercise: update an accessible link○Data attributes and conditional text○Exercise: announce session availability○Boolean attributes and DOM properties○Exercise: unlock a volunteer sign-up✦Module Quiz
○Add, remove, and check classes○Exercise: mark a favourite card○Toggle a panel accessibly○Exercise: toggle the help panel○Inline styles, classes, and hidden○Exercise: style and hide a notice●Change a CSS custom property from JavaScript○Exercise: change a workshop card accent✦Module Quiz
○Create and Append a Text Node○Exercise: Add a Reading List Item○Place Nodes Before and Between○Exercise: Order the Workshop Agenda○Remove, Replace, and Clear Safely○Exercise: Refresh a Museum Display○Clone a Card and Insert a Batch○Exercise: Clone Two Exhibit Cards✦Module Quiz
○Listen for Clicks with a Named Handler○Exercise: Check Library Hours○Event Target, Current Target, and Delegation○Exercise: Delegate Pantry Actions○Keyboard Events Without Trapping Keys○Exercise: Search the Recipe Box○Once, Remove, and Bubble○Exercise: Control Workshop Notifications✦Module Quiz
○Read a field while someone types○Build a live name preview○Handle submit without leaving the page○Validate a library request○Keep a selection in sync on change and reset○Sync a preference and its reset state○Read multiple checked values with FormData○Build a checkbox-based garden request✦Module Quiz
○Filter a list as someone types○Build a live trail finder○Toggle an accessible disclosure○Build a guide menu disclosure○Create and remove items with one delegated listener○Build a neighborhood task board○Sort a workshop table with accessible buttons○Build an accessible sortable resource table✦Module Quiz
○Read selectable cards and detail updates○Build directory cards and a selected profile○Trace live search and an empty state○Add live search to the community directory○Trace safe additions and delegated removal○Add and remove community directory cards✦Module Quiz
○Read and update a live itinerary○Build the workshop itinerary○Add a validated item through a form○Add a workshop session○Filter and remove live entries○Finish the workshop planner✦Module Quiz
○Fetch JSON and render safe text○Exercise: load recipe cards○Handle loading, empty, and failed responses○Exercise: handle alert states○Build a query with URLSearchParams○Exercise: search the catalog○Abort outdated requests○Exercise: keep the latest result✦Module Quiz
○Load a dashboard from an offline API fixture○Build an events dashboard○Query a dashboard with URLSearchParams○Add event search to the dashboard○Retry requests without stale results○Finish a resilient event dashboard✦Module Quiz

Change a CSS custom property from JavaScript

A night-market stall card needs an alternate accent color. Keep the border, badge, and other design rules in CSS; JavaScript should change just the shared color value.

One value, several CSS uses

In style.css, the card defines --accent and two declarations use var(--accent). A custom property name keeps its leading -- and hyphens in JavaScript: card.style.setProperty("--accent", "#b54435") sets an inline value that overrides the CSS default on that card. card.style.removeProperty("--accent") removes only that inline override; the default from .stall-card applies again. This is different from assigning an empty color to every individual rule. getComputedStyle(card).getPropertyValue("--accent").trim() can read the effective value when debugging; card.style.getPropertyValue reads only the inline override.

The completed script wires two buttons:

javascript
const card = document.querySelector("#stall-card");
const status = document.querySelector("#accent-status");
document.querySelector("#warm-accent").addEventListener("click", () => {
  card.style.setProperty("--accent", "#b54435");
  status.textContent = "Warm accent selected.";
});
document.querySelector("#default-accent").addEventListener("click", () => {
  card.style.removeProperty("--accent");
  status.textContent = "Default accent restored.";
});

The property is inherited by descendants, so the badge uses the card's current accent without any extra JavaScript. Unlike a class for a fixed theme, this technique also works when the accent value comes from a bounded, validated palette. Do not inject untrusted arbitrary CSS strings.

Try it in the preview

Run: the card border and badge start blue. Press Warm accent: both become brick red. Press Default accent: the inline override disappears and CSS's blue returns. Inspect the stylesheet to find both var(--accent) uses. Change the warm color to another valid hex color and Run to see both update, then restore it. Next, build a separate card with the same set/reset pattern.

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