[CSS] Blue line below the arrow

On some resolutions the blue line appear below the arrow. Also when I resize browser window.
How can I fix that?
https://static.livechatinc.com/8801096/P7S08YFE92/f586d6b63e426985d60cf26e39ba736e/Screen%20Shot%202018-04-11%20at%2015.18.14.png