How to reposition Chrome Developer Tools

Chrome 46 or newer

Click the vertical ellipsis button ( ⋮ ) then choose the desired docking option.

Chrome 45 or older

Long-hold the dock icon in the top right. It pops up an option to change the docking

To change the split between the HTML and CSS panels, go in DevTools to Settings (F1) > General > Appearance > Panel Layout.

Place your pointer on the dock button and long click it (some seconds) or right & left mouse click depending on the browser version.