http://ilkinulas.github.io/programming/2016/02/05/sublime-text-syntax-highlighting.html
~/.config/sublime-text/Packages/Theme - One Dark/One Dark.tmTheme
to create new syntax highlighting
create a new sublime syntax file that contains the scope of stuff
and then modify your tm theme which it will specify the scopes from your syntax file
<dict>
<key>scope</key>
<string>rust.custom.String</string>
<key>settings</key>
<dict>
<key>fontStyle</key>
<string>bold</string>
<key>foreground</key>
<string>#F7860A</string>
</dict>
</dict>
<dict>
<key>scope</key>
<string>rust.custom.let</string>
<key>settings</key>
<dict>
<key>fontStyle</key>
<string>bold</string>
<key>foreground</key>
<string>#204A87FF</string>
</dict>
</dict>