You can set the default browser size by running:

var width = 800;

var height = 600;

browser.driver.manage().window().setSize(width, height);

To maximize the browser window, run:

browser.driver.manage().window().maximize();

To set the position, run:

var x = 150;

var y = 100;

browser.driver.manage().window().setPosition(x, y);

If you get an error:

WebDriverError: unknown error: operation is unsupported with remote debugging

Operation not supported when using remote debugging Some WebDriver
commands (e.g. resizing the browser window) require a Chrome extension
to be loaded into the browser. ChromeDriver normally loads this
"automation extension" every time it launches a new Chrome session.

However ChromeDriver can be instructed to connect to an existing
Chrome session instead of launching a new one. This is done using
'debuggerAddress' in the Capabilities (aka ChromeOptions) object.
Since the automation extension is only loaded at startup, there are
some commands that ChromeDriver does not support when working with
existing sessions through remote debugging.

If you see the error "operation not supported when using remote
debugging", try rewriting the test so that it launches a new Chrome
session. This can be done by removing 'debuggerAddress' from the
Capabilities object.

Source: Operation not supported when using remote debugging