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.
Keyboard shortcut to toggle the docking position (side/bottom)
CTRL+SHIFT+D
And there are many shortcuts you can see them by going to
Settings » Shortcuts, as displayed here:
Alternatively, use CTRL + ? to go to the settings, from there one can reach the "Shortcuts" sub-item on the left or use the Official reference.