When editing a filter:
- "Switch editor" button (#mw-abusefilter-switcheditor element) has a display: inline; CSS.
- "Check syntax" button (#mw-abusefilter-syntaxcheck element) has a display: inline-block; CSS.
As a result, these buttons are not vertically aligned.
Explanation:
#mw-abusefilter-switcheditor is initially hidden: ext.abuseFilter.less#147. Then it is showed using jQuery: ext.abuseFilter.edit.js#517. Problem: the element being a <span>, jQuery adds it a display: inline; inline CSS.
Meanwhile, #mw-abusefilter-syntaxcheck has the initial display: inline-block; from OOUI:
.oo-ui-horizontalLayout > .oo-ui-widget { display: inline-block; vertical-align: middle; }
Screenshot attached.
