fix(style): introduce padding variable and fix slider padding

[silvester-pari]

Implemented changes

This PR improves the padding of the itemfilter and introduces a new CSS variable:

• padding is now done on a lower level, preventing white spaces around "separator lines"
• there is a new CSS variable called --padding with the default value 0.5rem; with this value the padding can be modified or completely disabled (set to 0)
• the randge slider has been fixed, removing unnecessary overflow and centering the slider on the available width

Screenshots/Videos

Before (no padding, padding set in parent app)

After (default padding, increased padding, no padding)

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [x] All checks have passed
• [x] The PR title follows conventional commit style and reflects the type of change (major/minor/patch, breaking)
• [x] The PR title describes the change within this element (each merged PR equals one entry in the element's changelog!)

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[lubojr]

Looks much leaner! Thank you