Linear gradient method
This method uses linear gradients. Be sure to submit it for production.
blockquote { background-image: linear-gradient(to right, rgba(41,137,216,0) 0%,rgba(37,131,210,0) 42%,rgba(37,131,210,1) 42%,rgba(36,129,208,1) 58%,rgba(36,129,208,0) 58%,rgba(32,124,202,0) 99%); background-position: top; background-size: 100% 8px; background-repeat: no-repeat; }
Background Image Method
If you prefer a fixed width of the blue strip and resizable, you can use base64-encoded 1 pixel image as the background instead, as suggested by @Joint.
blockquote { background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNUabzwHwAEvAJ2QlOyvQAAAABJRU5ErkJggg==); background-position: top; background-size: 120px 8px; background-repeat: no-repeat; }
You can change the background-size to whatever you need.

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