Is it possible to make topo layer lines more bold and different color through js or any other way.
Currently It looks like this
AFAIK, ESRI hasn't yet released any vector based global elevation contour dataset (at least, I haven't been able to find it on ArcGIS Online). The contours you see in the base topographic map are baked into the raster layer, and can thus not be separately styled.
It would be nice to have access to a global vector tile elevation contour dataset for styling purposes, but I think ESRI fears the load this would put on their systems if usage soared, as vector contour datasets are heavy stuff in terms of file sizes and vertex complexity.
How to access global vector tile elevation contour dataset through arcgis online, in online styling it gives only elevation spot. or is their any other layer which have countour editable for styling
As I said, as far as I know, ESRI hasn't released any global vector based contour dataset that could be used for custom styling. If there are contours in a vector tile layer visible, it is usually baked into the raster hillshade that accompanies the vector layers. So you will probably have to generate and host such dataset yourself if you have a need. There are several sources of global DEM available, but it will be quite a bit of work and hassle to create a vector contour dataset of it on a global scale.
Such global vector contour datasets are huge by the way. I think I read that the developer of OpenTopoMap had to create a vector contour data dataset somewhere in the range of 1TB or so, to cover the globe.
If you do manage to find Vector Tiles of the contours for you area of interest you can use the ArcGIS Vector Tile Style editor to visualize them as you desire.
ArcGIS Vector Tile Style Editor
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