The Kunena team has announce the arrival of Kunena 6.3.0 [K 6.3.0] in stable which is now available for download as a native Joomla extension for J! 4.4.x/5.0.x/5.1.x. This version addresses most of the issues that were discovered in K 6.2 and issues discovered during the last development stages of K 6.3
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I can see, from the image, that the joomagic.com Joomla template has overridden a lot of the Kunena template CSS rules. The Joomla template seems to be responsible for your buttons not rendering properly. I would imagine that other buttons would also appear like you have shown. Use Firebug for Firefox to examine and correct the button rendering problem. Without seeing your website there's nothing more I can do for you.
I can see, from the image, that the joomagic.com Joomla template has overridden a lot of the Kunena template CSS rules. The Joomla template seems to be responsible for your buttons not rendering properly. I would imagine that other buttons would also appear like you have shown. Use Firebug for Firefox to examine and correct the button rendering problem. Without seeing your website there's nothing more I can do for you.
Thanks for help. Editing style.css solved my problem.