Fix Fast Vertical Slider CSS

[MarcSkovMadsen]

Fixes #3003

You can verify via

import panel as pn
import panel.widgets as pnw

horizontal = pnw.FloatSlider(name='Horizontal', value=0, step=0.05, start=0, end=1)
vertical = pnw.FloatSlider(name='Vertical', value=0, step=0.05, start=0, end=1, orientation='vertical')

template = pn.template.FastListTemplate(
    title="FastListTemplate",
    main=[horizontal, vertical]).servable()

[philippjfr]

I'm not a huge fan of how thin the actual slider is. Can we maybe use this opportunity to tweak that a little bit? The original fast slider isn't that thin either.

[MarcSkovMadsen]

I've made it larger

[philippjfr]

Looks much better to me, thanks for the fix!