How to reproduce:
1. Open the attached “IN-117482” project
2. In the Menu field, select the “Test → TextFieldTest” property
3. Observe the pop-up “TextFieldTest” window. Notice that TextInput field fills the entire window
4. In the Project tab, open the “TextFieldTest” script
5. Uncomment line 14, “multiline = true”
6. Save the changes
7. Observe the pop-up “TextFieldTest” window

Expected result: The TextInput element fills the entire space
Actual result: The TextInput element does not fill the entire space

Reproducible with: 6000.0.0b11 (a707ca4efec4), 6000.0.59f2, 6000.2.8f1, 6000.3.0b6, 6000.4.0a2
Not reproducible with: 2022.3.67f2, 2023.3.0b10

Reproducible on: macOS 15.3.2 (24D81) (M1 Max)
Not reproducible on: No other environments tested

Notes:

• Also reproducible when constrained sizing is used
• When “multiline = true”, the “align-self” property is added to TextInput element USS styles and set to “FlexStart”, which causes this issue. Changing it to “Stretch” or “Auto” resolves the problem