The ornamental design for smart toilet lid, as shown and described.
1.-2. Smart toilet lid
1.1 : Front
1.2 : Back
1.3 : Left
1.4 : Right
1.5 : Top
1.6 : Bottom
1.7 : Perspective
2.1 : Perspective
2.2 : Unfolded
1.1 is a front elevation view of a first embodiment of a smart toilet lid; 1.2 is a rear elevation view thereof; 1.3 is a left side elevation view thereof; 1.4 is a right side elevation view thereof; 1.5 is a top plan view thereof; 1.6 is a bottom plan view thereof; 1.7 is a perspective view thereof; 2.1 is a perspective view of a second embodiment of a smart toilet lid showing our new design; and 2.2 is a use state view thereof.