
.ck-editor__editable {
width: 700px;
min-height: 400px;
}
I've configured editor's size, but toolbar's width isn't changed.
How can I set the with of toolbar and editor same?
@Luberen You should style the top-most container of the editor, like:
.ck.ck-editor {
max-width: 700px
}
See below (I've set 500px there):

To avoid confusion I've added an answer about controlling width to the @wwalc's question about configuring height of the editor.
@jodator Thanks. I have one more question. Is it impossible to change minimum height? After I changed class selector to .ck.ck-editor, height of the editor has been reduced.
@Luberen you should be able to set min-height on the .ck-editor__editable as in the SO answer. As you control height/width of the editor with CSS the proper selectors for configuring would be:
.ck.ck-editor for width (whole toolbar + editing area).ck-editor__editable - for height (it will set the height of the editing area so it will not mess with toolbar's height)