Use comma as separator. Supported formats

• WxH (eg. 100x50) - crop to WxH viewbox (from center)
• WxHt (eg. 100x50t) - crop to WxH viewbox (from top)
• WxHb (eg. 100x50b) - crop to WxH viewbox (from bottom)
• WxHf (eg. 100x50f) - fit inside a WxH viewbox (without cropping)
• 0xH (eg. 0x50) - resize to H height preserving the aspect ratio
• Wx0 (eg. 100x0) - resize to W width preserving the aspect ratio