Fix font color in search input box (#1524)

* Fix color

* Use --pst-color-text-base

Author: harupy

src/pydata_sphinx_theme/assets/styles/components/_search.scss

@@ -53,6 +53,7 @@
 
 .form-control {
   background-color: var(--pst-color-background);
+  color: var(--pst-color-text-base);
 
   &:focus,
   &:focus-visible {