Menus and dropdowns garbled -- repeating horizontal lines obscure text

Anyone have suggestions on what might be causing this?

Horizontal lines repeat across both application menus and settings drop-down menus. Lines get progressively longer, obscuring more text, moving right to left. So, for example, the lines over the “Debugger” menu amount to dashes, while the lines over the “File” menu easily obscure eight characters at a span. Likewise, unlike the Syntax Theme dropdown (pictured above), the UI Theme dropdown is almost entirely obscured by three wide columns of horizontal lines with negligible padding between them.

Menu example.