What collateral is used for long and short trades?

In isolated margin mode, long trades use the contract's base token as collateral, while short trades use a stablecoin as collateral. For example, in the SOLUSD contract, going long requires SOL as collateral, and going short requires a stablecoin supported by the platform, such as USDC. In cross margin mode, you only need to deposit your assets into the Portfolio, and you can use the available balance to go long or short in any contract.