The abbreviation CSS can stand for any of several things:

• Calderbank-Shor-Steane codes: class of quantum error-correcting codes.
• Cascading Style Sheets: used to format XHTML, HTML and XML documents.
• Catalina Sky Survey
• Chicago SouthShore and South Bend Railroad
• Closed source software: as opposed to open source software
• Confederate States Ship
• Content-scrambling system: an encryption algorithm used primarily on DVDs.
• Core System Software
• Counter-Strike:Source: the multiplayer CS game updated for the source engine released with Half-Life 2
• CSS Profile: an application distributed by the College Board allowing students to apply for financial aid