diff --git a/overlayer.js b/overlayer.js
index 880b906..6fd03ab 100644
--- a/overlayer.js
+++ b/overlayer.js
@@ -127,8 +127,8 @@ export class Overlayer {
         const { color = 'red' } = options
         const g = createSVGElement('g')
         g.setAttribute('fill', color)
-        g.style.opacity = `var(--overlayer-highlight-opacity, .3)`
-        g.style.mixBlendMode = `var(--overlayer-highlight-blend-mode, normal)`
+        g.style.opacity = 'var(--overlayer-highlight-opacity, .3)'
+        g.style.mixBlendMode = 'var(--overlayer-highlight-blend-mode, normal)'
         for (const { left, top, height, width } of rects) {
             const el = createSVGElement('rect')
             el.setAttribute('x', left)