Does acquiring some writing tools, in excess of the workplace's needs, for home use count as theft, given that there is no intention of stealing and the employee believes they are abundant and exceed the work's requirements?

The tools and public property placed under your charge are a trust that must be preserved and used only for their designated purpose, as Allah Almighty says: "Indeed, Allah commands you to render trusts to whom they are due." Therefore, it is not permissible to take them home or use them for personal work, as that is a betrayal of the trust. If anything remains of them, you must return it to the person in charge or inform him about it. There is no harm in using them if you are given permission by someone authorized to do so.