style form in sidebar widget

Hi folks,

can i change the styling of the form in the sidebar widget so that it look more like this:

https://drive.google.com/file/d/1oNrL-BSKwVnEdvpT-aejfHQkgQ8Kv6BG/view?usp=sharing

placeholder text to the left,
margin between boxes smaller,
button square and full width

(I have some overall custom css for the button, so the css needs to adress the sidebar only)

see link to my site in private section

Many thanks,

Alexander