Add Create A Pulsing Background With CSS Animation as a css til

css/create-a-pulsing-background-with-css-animation.md

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+# Create A Pulsing Background With CSS Animation
+
+You can create a smoothly pulsing background effect with CSS animations. This
+can be achieved by defining a set of keyframes that start at one background
+color, transitions to another color, and then transitions back to the original
+color.
+
+```css
+@keyframes pulse {
+  0%, 100% {
+    background-color: #f56a3f;
+  }
+  50% {
+    background-color: #9e42b0;
+  }
+}
+```
+
+At the beginning (`0%`) and end (`100%`) we declare the background color to be
+`#f56a3f`. Halfway through (`50%`) it should be `#9e42b0`. The browser will
+animate everything in between.
+
+This can then be applied infinitely with a lengthy duration to give it a real
+smooth feel.
+
+```css
+body {
+  animation: pulse 20s infinite;
+}
+```
+
+Here is a [live example](https://codepen.io/jbranchaud/pen/vYYqQjO).
+
+[source](https://css-tricks.com/almanac/properties/a/animation/)