Issue #3521869 by mably, thamas: Allow usage of a CSS variable for the sticky offset setting

Closes #3521869

assets/js/tocjs.js

@@ -314,39 +314,6 @@
     return 1;
   }
 
-  /**
-   * Retrieves the value of a CSS property from a CSS variable.
-   *
-   * If the CSS variable contains a fallback value, it will be used
-   * if the CSS variable is not defined.
-   *
-   * @param {string} styleValueSetting - The value of the CSS variable or a string containing `var(--variable, fallback)`.
-   * @param {string} [containerSelector='body'] - The selector for the container element to retrieve the CSS variable from.
-   * @return {string} - The value of the CSS property or the fallback value if defined.
-   */
-  function getStyleValueFromCssProperty(
-    styleValueSetting,
-    containerSelector = 'body',
-  ) {
-    let styleValue = styleValueSetting;
-    // Check if it's a CSS variable reference with optional fallback.
-    const variableMatch = styleValueSetting.match(
-      /^var\((--[a-zA-Z0-9-_]+)(?:,\s*([^)]+))?\)$/,
-    );
-    if (variableMatch) {
-      const propertyName = variableMatch[1];
-      const fallback = variableMatch[2]?.trim();
-      const container = document.querySelector(containerSelector);
-      styleValue = getComputedStyle(container)
-        .getPropertyValue(propertyName)
-        .trim();
-      if (!styleValue && fallback) {
-        styleValue = fallback;
-      }
-    }
-    return styleValue;
-  }
-
   /**
    * @param {TocObject} tocObj - The tocObj object.
    */
@@ -360,15 +327,6 @@
     $tocNav.find('ul').remove();
     let lastLi = $tocNav[0];
 
-    // Determine scroll offset.
-    let scrollToOffset;
-    if (opts.scrollToOffset) {
-      scrollToOffset = getStyleValueFromCssProperty(
-        opts.scrollToOffset,
-        opts.container || 'body',
-      );
-    }
-
     $headings.each((i, heading) => {
       // Skip invisible headings if specified in configuration.
       if (opts.skipInvisibleHeadings) {
@@ -385,8 +343,8 @@
       }
 
       // Apply scroll offset.
-      if (scrollToOffset) {
-        heading.style.scrollMarginTop = scrollToOffset;
+      if (opts.scrollToOffset) {
+        heading.style.scrollMarginTop = opts.scrollToOffset;
       }
 
       // build TOC item