use the below code which is accepted for changing the height the commented code is accepting for the particular element in the inspection window but default height set for the text area is 38px; if u change in the properties of a textarea element but text area height is not changing in UI.
height: 30px !important;
but for the text field above code is accepting you can add the class txt to the feild.
hope it helps.
Inside the properties for the textarea you can change it to 1 lines.
If you want to change it through CSS only, it would be hard because the “Number of lines" command seems to apply a ‘style’ onto the element which is the highest priority when it comes to CSS-styling like shown in your picture.