Dress
The traditional dress in Sri Lanka is still commonly worn today, although there is a slow shift to wearing more western-styled clothing. No matter which style the people wear, they tend to dress somewhat conservatively as long pants and shirts are common. Among the more traditional clothes are colorful saris for women and sarongs without a shirt for men. The sarong is a long piece of cloth worn around the waist in the place of western-styled pants. A sari is similar to a sarong in that it is a large piece of cloth delicately wrapped, but the sari is used to cover a woman's entire body.
Today the sarong is still commonly worn by men in Sri Lanka, but t-shirts are often coupled with them and in more formal occasions pants are the norm. Men also tend to wear a shirt called a baniyama, generally worn by the Sinhalese, or a patta vetty, generally worn by the Tamils. Likewise, women also commonly wear the sari, but again have aspects of western-styled clothing. Today the people wear aspects of their traditional clothes alone, western-clothes alone, or a combination of both. This is very dependent on personal tastes, situation, and to a degree age, as the older generation is rarely seen wearing western-styled clothing, while many young people exclusively wear western-styled clothing.
No matter the style, the dress in Sri Lanka is fairly conservative. While the Muslim population tends to dress this way for religious reasons, most people dress like this due to culture, not because there is anything "wrong" with dressing any other way. For this reason, wearing shorts or short sleeve shirts will make you look odd in the local's eyes, but it will not be offensive unless in a religious building, a business meeting, or with a conservative Muslim (there are few in Sri Lanka). In temples and other holy sites you are expected to cover your knees, shoulders, and preferably elbows, although the actual length of your clothing may vary from site to site. Additionally, if you know you are meeting Muslims or Hindus, try to cover up as they both find it rude or even slightly offensive to show too much skin.