Fix too small magnifier

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/1092

As a result of earlier redesign, the magnifier ended
up being too small. The size of the magnifier will now
be dependent on the default font size instead of the
parent font size.

src/css/document-blocked.css

@@ -63,6 +63,7 @@ a {
     color: var(--fg-0-60);
     cursor: pointer;
     fill: var(--fg-0-60);
+    font-size: 1rem;
     padding: var(--default-gap-xxsmall);
     position: absolute;
     transform: translate(0, -50%);