Merge pull request #2693 from odsantos/css-animations-typo

Fix typo.

Author: iliakan

7-animation/2-css-animations/article.md

@@ -433,7 +433,7 @@ The `transform` property is a great choice, because:
 
 In other words, the browser calculates the Layout (sizes, positions), paints it with colors, backgrounds, etc at the Paint stage, and then applies `transform` to element boxes that need it.
 
-Changes (animations) of the `transform` property never trigger Layout and Paint steps. More than that, the browser  leverages the graphics accelerator (a special chip on the CPU or graphics card) for CSS transforms, thus making them very effecient.
+Changes (animations) of the `transform` property never trigger Layout and Paint steps. More than that, the browser  leverages the graphics accelerator (a special chip on the CPU or graphics card) for CSS transforms, thus making them very efficient.
 
 Luckily, the `transform` property is very powerful. By using `transform` on an element, you could rotate and flip it, stretch and shrink it, move it around, and [much more](https://developer.mozilla.org/docs/Web/CSS/transform#syntax). So instead of `left/margin-left` properties we can use `transform: translateX(…)`, use `transform: scale` for increasing element size, etc.