In case someone else needs the answer, the code is found in Atahualpa Options under “Add HTML/CSS Inserts” under “CSS Inserts”. It says:
div#imagecontainer {
border-top: solid; 5px; #000000;
border-bottom: solid; 5px; #000000
}
To fix it, just remove the “solid; 5px; #000000;” part after both border-top and border-bottom.
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