refactor: Replace white & black colors with theme aware ones

Signed-off-by: Carlos Esteban Lopez <lcarlosesteb@vmware.com>

plugins/code-coverage/src/components/FileExplorer/CodeRow.tsx

@@ -29,7 +29,7 @@ const useStyles = makeStyles(theme => ({
     width: '50px',
     borderRight: `1px solid ${theme.palette.grey[500]}`,
     textAlign: 'center',
-    color: 'white', // need to enforce this color since it needs to stand out against colored background
+    color: theme.palette.common.white, // need to enforce this color since it needs to stand out against colored background
     paddingLeft: theme.spacing(1),
     paddingRight: theme.spacing(1),
   },

plugins/code-coverage/src/components/FileExplorer/FileContent.tsx

@@ -37,7 +37,7 @@ const useStyles = makeStyles(theme => ({
     margin: 'auto',
     top: '2em',
     width: '80%',
-    border: '2px solid #000',
+    border: `2px solid ${theme.palette.common.black}`,
     boxShadow: theme.shadows[5],
     padding: theme.spacing(2, 4, 3),
     overflow: 'scroll',