[UI Classic] Add Invisible line/border for resizing margins

[zeoint]

• If one wants to Resize the margins of media list and item list, one needs to go down to the resizer icon to do it.
• My suggestion / request is to add a hidden line at the end of scroll bar of each list.
• The user can grab the corner to resize the lists rather than holding the resize icon to resize the list.
• Example of the feature request can be seen in the image below.

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[Sheepux]

Ultra low priority. The resize is here thanks to the css resize property. Adding border handlers is an extra work (not css native)

[Sheepux]

Almost done, i still need to find a correct color/design.

[Sheepux]

completed by 0d4c2f8