Image of Overleaf. Line 15 of the source code is highlighted with a pink background. Below this (obscuring the code on lines 16 to 21) is a box with a red outline that contains the error message:
Undefined control sequence.
l.15 ...xample document. Modified: \pdcreationdate
At the top right above the preview pane is a drop-down menu labelled "compile error" and the two items are displayed in a box with a pink background:
go to first error / warning
open latex log