The tools are opened on the bottom of the chrome window per default. This is a rather bad choice for a wide screen display since there is plenty of empty space to the right
Click the vertical ellipsis button ( ⋮ ) then choose the desired docking option.
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.