Hi Linda, Kimberly here from landscape-solutions-for-you. Thank you for asking the question on your Croton plant in the container.
There are a couple of things that come to mind with the Croton species and their leaves turnng brown. Croton can be drought tolerant. If you are watering often, consider reducing the amount of water. If the soil is old, consider changing out the potting soil. You can use a light weight potting soil, and since this is a tropical plant, add some sand to the potting soil.
Make sure the plant has sun light, but also can take some shade or filtered light.
See if these suggestions help your Croton. Remove the brown leaves. Unless your Croton has fungus or a disease, by changing the potting soil, watch the watering, and make sure the lighting is correct, the plant should be fine.
I hope this helps some and you get your Croton plant healthy again. Keep us informed how the Croton is doing. Thanks for asking your question and feel free to ask a question anytime here at landscape solutions for you. Have a great day.
Kimberly