Is taking money from the company's safe without permission—due to a low and insufficient salary—considered theft and unlawful (haram)?

It is not permissible for an employee to take anything from the shop's till if a specific wage has been agreed upon. If he does so, he is disobedient and a betrayer of trust, and his action is considered unlawful theft. He must repent by returning the money or seeking forgiveness from its owner, based on the hadith narrated by Al-Bukhari: "Whoever has wronged his brother concerning his honor or anything else, let him seek his forgiveness today before there will be no Dinar or Dirham." And the hadith narrated by Al-Tirmidhi: "The hand is responsible for what it takes until it returns it." It is advisable to be pious, for piety brings abundant provision, as Allah Almighty says: "And whoever fears Allah - He will make for him a way out And will provide for him from where he does not expect." Provision is only attained through obedience to Allah.