The words opposite and across from mean that something is located at the other side of something.

The bank is opposite the post office. or The bank is across from the post office.

Henry sat opposite me at the table. or Henry sat across from me at the table.

The expression in front of simply means that one thing is closer to a point of reference (the "front" of an area, or the point of view of the person looking).

I stood in front of the bank.

He sat in front of me in the classroom.

The word before can be used for location/position, but it is somewhat rare and more formal. Instead, before is typically used for time or for position in a sequence:

We need to pack our bags before leaving for the airport.

The letter i comes before the letter e in the word "friend." or position in a sequence

The Worlds Most Beautiful Buildings

TAJ MAHAL INDIA

Is this the worlds most famous building? And its most romantic (ignoring the sprawling, industrial city around it, and the hordes of rickshaw-wallahs and touts)? Described by Indian poet Rabindranath Tagore as a teardrop on the face of eternity, the Taj Mahal in Agra was built by Emperor Shah Jahan as a memorial for his second wife, Mumtaz Mahal, who died giving birth to their 14th child in 1631. Its an extravagant, whitemarble monument to love, which may explain all the young, starry-eyed couples wandering around it.