Clean up the "toggle source" link

[nithinbekal]

When the method param sequence is too long, the "toggle source" link can overlap the method params. The text for this link is also quite verbose - "click to toggle source".

What's changed?

• Changes the link text from "click to toggle source" to "Toggle source"
• Keeps the link always visible, rather than only showing up on hover
• Removes the zoom image which takes up more space
• Makes minor changes to the typography of the text to make it easier to read

Screenshots

Before

After

[st0012]

Thanks for the PR, but I already included a similar change in the overhaul on method source toggle in #1176