Users which have devices with Android system recently received update of Twitter app. After the newest update Twitter completely changes its look, including changing of navigation bar's location which now is located on the bottom. What's interesting, update was done by creators on Twitter's servers, so you don't have to download additional package of data from Google Play Store.
The most important change in this update is previously mentioned changed location of navigation bar, which now is located on the bottom. Improvement is dedicated for people with smartphones which have big screens - after update use of Twitter's app on these phones should be much more comfortable. However, some parts of user interface are still located on the top of screen including search bar, but in overall this update seems to be interesting improvement.